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## The SQLite Virtual Machine

### Introduction

In order to execute an SQL statement, the SQLite library first parses the SQL, analyzes the statement, then generates a short program to execute the statement. The program is generated for a "virtual machine" implemented by the SQLite library. That virtual machine is sometimes called the "VDBE" or "Virtual DataBase Engine". This document describes the operation of the VDBE.

This document is intended as a reference, not a tutorial. A separate Virtual Machine Tutorial is available. If you are looking for a narrative description of how the virtual machine works, you should read the tutorial and not this document. Once you have a basic idea of what the virtual machine does, you can refer back to this document for the details on a particular opcode. Unfortunately, the virtual machine tutorial was written for SQLite version 1.0. There are substantial changes in the virtual machine for version 2.0 and again for version 3.0.0 and again for version 3.5.5 and the tutorial document has not been updated. But the basic concepts behind the virtual machine still apply.

The source code to the virtual machine is in the vdbe.c source file. All of the opcode definitions further down in this document are contained in comments in the source file. In fact, the opcode table in this document was generated by scanning the vdbe.c source file and extracting the necessary information from comments. So the source code comments are really the canonical source of information about the virtual machine. When in doubt, refer to the source code.

Each instruction in the virtual machine consists of an opcode and up to five operands named P1, P2 P3, P4, and P5. The P1, P2, and P3 operands are 32-bit signed integers. These operands often refer to registers but can also be use dfor other purposes. The P1 operand is usually the cursor number for opcodes that operate on cursors. P2 is usually the jump destination jump instructions. P4 may be a 32-bit signed integer, a 64-bit signed integer, a 64-bit floating point value, a string literal, a Blob literal, a pointer to a collating sequence comparison function, or a pointer to the implementation of an application-defined SQL function, or various other things. P5 is an unsigned character normally used as a flag. Some operators use all five operands. Some use one or two. Some operators use none of the operands.

The virtual machine begins execution on instruction number 0. Execution continues until a Halt instruction is seen, or until the program counter becomes one greater than the address of last instruction, or there is an execution error. When the virtual machine halts, all memory that it allocated is released and all database cursors it may have had open are closed. If the execution stopped due to an error, any pending transactions are terminated and changes made to the database are rolled back.

The virtual machine can have zero or more cursors. Each cursor is a pointer into a single table or index within the database. There can be multiple cursors pointing at the same index or table. All cursors operate independently, even cursors pointing to the same indices or tables. The only way for the virtual machine to interact with a database file is through a cursor. Instructions in the virtual machine can create a new cursor (OpenRead or OpenWrite), read data from a cursor (Column), advance the cursor to the next entry in the table (Next) or index (NextIdx), and many other operations. All cursors are automatically closed when the virtual machine terminates.

The virtual machine contains an arbitrary number of registers with addresses beginning at one and growing upward. Each register can a single SQL value (a string, a BLOB, a signed 64-bit integer, a 64-bit floating point number, or a NULL). A register might also hold objects used internally by SQLite, such as a RowSet or Frame.

### Viewing Programs Generated By SQLite

Every SQL statement that SQLite interprets results in a program for the virtual machine. But if you precede the SQL statement with the keyword EXPLAIN the virtual machine will not execute the program. Instead, the instructions of the program will be returned like a query result. This feature is useful for debugging and for learning how the virtual machine operates. For example:

>     $ sqlite3 ex1.db
>     sqlite> .explain
>     sqlite> explain delete from tbl1 where two<20;
>     addr  opcode         p1    p2    p3    p4             p5  comment
>     ----  -------------  ----  ----  ----  -------------  --  -------------
>     0     Trace          0     0     0                    00
>     1     Goto           0     23    0                    00
>     2     Null           0     1     0                    00  r[1]=NULL
>     3     OpenRead       0     2     0     2              00  root=2 iDb=0; tbl1
>     4     Explain        0     0     0     SCAN TABLE tbl1  00
>     5     Noop           0     0     0                    00  Begin WHERE-loop0: tbl1
>     6     Rewind         0     14    0                    00
>     7       Column         0     1     2                    00  r[2]=tbl1.two
>     8       Ge             3     13    2     (BINARY)       6a  if r[3]>=r[2] goto 13
>     9       Noop           0     0     0                    00  Begin WHERE-core
>     10      Rowid          0     4     0                    00  r[4]=rowid
>     11      RowSetAdd      1     4     0                    00  rowset(1)=r[4]
>     12      Noop           0     0     0                    00  End WHERE-core
>     13    Next           0     7     0                    01
>     14    Noop           0     0     0                    00  End WHERE-loop0: tbl1
>     15    Close          0     0     0                    00
>     16    OpenWrite      0     2     0     3              00  root=2 iDb=0; tbl1
>     17      RowSetRead     1     21    4                    00  r[4]=rowset(1)
>     18      NotExists      0     20    4     1              00  intkey=r[4]
>     19      Delete         0     1     0     tbl1           00
>     20    Goto           0     17    0                    00
>     21    Close          0     0     0                    00
>     22    Halt           0     0     0                    00
>     23    Transaction    0     1     0                    00
>     24    VerifyCookie   0     1     0                    00
>     25    TableLock      0     2     1     tbl1           00  iDb=0 root=2 write=1
>     26    Integer        20    3     0                    00  r[3]=20
>     27    Goto           0     2     0                    00

All you have to do is add the EXPLAIN keyword to the front of the SQL statement. But if you use the ".explain" command in the CLI, it will set up the output mode to make the VDBE code easier for humans to read.

When SQLite is compiled with the SQLITE_DEBUG compile-time option, extra PRAGMA commands are available that are useful for debugging and for exploring the operation of the VDBE. For example the vdbe_trace pragma can be enabled to cause a disassembly of each VDBE opcode to be printed on standard output as the opcode is executed. These debugging pragmas include:

- PRAGMA parser_trace
- PRAGMA vdbe_addoptrace
- PRAGMA vdbe_debug
- PRAGMA vdbe_listing
- PRAGMA vdbe_trace

### The Opcodes

There are currently 151 opcodes defined by the virtual machine. All currently defined opcodes are described in the table below. This table was generated automatically by scanning the source code from the file vdbe.c.

Remember: The VDBE opcodes are not part of the interface definition for SQLite. The number of opcodes and their names and meanings are subject to change from one release of SQLite to the next.

Opcode Name | Description
--- | ---
Add | Add the value in register P1 to the value in register P2 and store the result in register P3. If either input is NULL, the result is NULL.
AddImm | Add the constant P2 to the value in register P1. The result is always an integer. To force any register to be an integer, just add 0.
Affinity | Apply affinities to a range of P2 registers starting with P1. P4 is a string that is P2 characters long. The nth character of the string indicates the column affinity that should be used for the nth memory cell in the range.

AggFinal

Execute the finalizer function for an aggregate. P1 is the memory location that is the accumulator for the aggregate.

P2 is the number of arguments that the step function takes and P4 is a pointer to the FuncDef for this function. The P2 argument is not used by this opcode. It is only there to disambiguate functions that can take varying numbers of arguments. The P4 argument is only needed for the degenerate case where the step function was not previously called.

AggStep | Execute the step function for an aggregate. The function has P5 arguments. P4 is a pointer to the FuncDef structure that specifies the function. Use register P3 as the accumulator. The P5 arguments are taken from register P2 and its successors.
And | Take the logical AND of the values in registers P1 and P2 and write the result into register P3. If either P1 or P2 is 0 (false) then the result is 0 even if the other input is NULL. A NULL and true or two NULLs give a NULL output.
AutoCommit | Set the database auto-commit flag to P1 (1 or 0). If P2 is true, roll back any currently active btree transactions. If there are any active VMs (apart from this one), then a ROLLBACK fails. A COMMIT fails if there are active writing VMs or active VMs that use shared cache. This instruction causes the VM to halt.
BitAnd | Take the bit-wise AND of the values in register P1 and P2 and store the result in register P3. If either input is NULL, the result is NULL.
BitNot | Interpret the content of register P1 as an integer. Store the ones-complement of the P1 value into register P2. If P1 holds a NULL then store a NULL in P2.
BitOr | Take the bit-wise OR of the values in register P1 and P2 and store the result in register P3. If either input is NULL, the result is NULL.
Blob | P4 points to a blob of data P1 bytes long. Store this blob in register P2.
Cast | Force the value in register P1 to be the type defined by P2. <ul> <li value="97"> TEXT <li value="98"> BLOB <li value="99"> NUMERIC <li value="100"> INTEGER <li value="101"> REAL </ul> A NULL value is not changed by this routine. It remains NULL.

Checkpoint

Checkpoint database P1. This is a no-op if P1 is not currently in WAL mode. Parameter P2 is one of SQLITE_CHECKPOINT_PASSIVE, FULL or RESTART. Write 1 or 0 into mem[P3] if the checkpoint returns SQLITE_BUSY or not, respectively. Write the number of pages in the WAL after the checkpoint into mem[P3+1] and the number of pages in the WAL that have been checkpointed after the checkpoint completes into mem[P3+2]. However on an error, mem[P3+1] and mem[P3+2] are initialized to -1.

Clear

Delete all contents of the database table or index whose root page in the database file is given by P1. But, unlike Destroy, do not remove the table or index from the database file.

The table being clear is in the main database file if P2==0. If P2==1 then the table to be clear is in the auxiliary database file that is used to store tables create using CREATE TEMPORARY TABLE.

If the P3 value is non-zero, then the table referred to must be an intkey table (an SQL table, not an index). In this case the row change count is incremented by the number of rows in the table being cleared. If P3 is greater than zero, then the value stored in register P3 is also incremented by the number of rows in the table being cleared.

See also: Destroy

Close | Close a cursor previously opened as P1. If P1 is not currently open, this instruction is a no-op.

CollSeq

P4 is a pointer to a CollSeq struct. If the next call to a user function or aggregate calls sqlite3GetFuncCollSeq(), this collation sequence will be returned. This is used by the built-in min(), max() and nullif() functions.

If P1 is not zero, then it is a register that a subsequent min() or max() aggregate will set to 1 if the current row is not the minimum or maximum. The P1 register is initialized to 0 by this instruction.

The interface used by the implementation of the aforementioned functions to retrieve the collation sequence set by this opcode is not available publicly, only to user functions defined in func.c.

Column

Interpret the data that cursor P1 points to as a structure built using the MakeRecord instruction. (See the MakeRecord opcode for additional information about the format of the data.) Extract the P2-th column from this record. If there are less that (P2+1) values in the record, extract a NULL.

The value extracted is stored in register P3.

If the column contains fewer than P2 fields, then extract a NULL. Or, if the P4 argument is a P4_MEM use the value of the P4 argument as the result.

If the OPFLAG_CLEARCACHE bit is set on P5 and P1 is a pseudo-table cursor, then the cache of the cursor is reset prior to extracting the column. The first Column against a pseudo-table after the value of the content register has changed should have this bit set.

If the OPFLAG_LENGTHARG and OPFLAG_TYPEOFARG bits are set on P5 when the result is guaranteed to only be used as the argument of a length() or typeof() function, respectively. The loading of large blobs can be skipped for length() and all content loading can be skipped for typeof().

Compare

Compare two vectors of registers in reg(P1)..reg(P1+P3-1) (call this vector "A") and in reg(P2)..reg(P2+P3-1) ("B"). Save the result of the comparison for use by the next Jump instruct.

If P5 has the OPFLAG_PERMUTE bit set, then the order of comparison is determined by the most recent Permutation operator. If the OPFLAG_PERMUTE bit is clear, then register are compared in sequential order.

P4 is a KeyInfo structure that defines collating sequences and sort orders for the comparison. The permutation applies to registers only. The KeyInfo elements are used sequentially.

The comparison is a sort comparison, so NULLs compare equal, NULLs are less than numbers, numbers are less than strings, and strings are less than blobs.

Concat | Add the text in register P1 onto the end of the text in register P2 and store the result in register P3. If either the P1 or P2 text are NULL then store NULL in P3. P3 = P2 || P1 It is illegal for P1 and P3 to be the same register. Sometimes, if P3 is the same register as P2, the implementation is able to avoid a memcpy().
Copy | Make a copy of registers P1..P1+P3 into registers P2..P2+P3. This instruction makes a deep copy of the value. A duplicate is made of any string or blob constant. See also SCopy.
Count | Store the number of entries (an integer value) in the table or index opened by cursor P1 in register P2
CreateIndex | Allocate a new index in the main database file if P1==0 or in the auxiliary database file if P1==1 or in an attached database if P1>1. Write the root page number of the new table into register P2. See documentation on CreateTable for additional information.
CreateTable | Allocate a new table in the main database file if P1==0 or in the auxiliary database file if P1==1 or in an attached database if P1>1. Write the root page number of the new table into register P2 The difference between a table and an index is this: A table must have a 4-byte integer key and can have arbitrary data. An index has an arbitrary key but no data. See also: CreateIndex

Delete

Delete the record at which the P1 cursor is currently pointing.

The cursor will be left pointing at either the next or the previous record in the table. If it is left pointing at the next record, then the next Next instruction will be a no-op. Hence it is OK to delete a record from within a Next loop.

If the OPFLAG_NCHANGE flag of P2 is set, then the row change count is incremented (otherwise not).

P1 must not be pseudo-table. It has to be a real table with multiple rows.

If P4 is not NULL, then it is the name of the table that P1 is pointing to. The update hook will be invoked, if it exists. If P4 is not NULL then the P1 cursor must have been positioned using NotFound prior to invoking this opcode.

Destroy

Delete an entire database table or index whose root page in the database file is given by P1.

The table being destroyed is in the main database file if P3==0. If P3==1 then the table to be clear is in the auxiliary database file that is used to store tables create using CREATE TEMPORARY TABLE.

If AUTOVACUUM is enabled then it is possible that another root page might be moved into the newly deleted root page in order to keep all root pages contiguous at the beginning of the database. The former value of the root page that moved - its value before the move occurred - is stored in register P2. If no page movement was required (because the table being dropped was already the last one in the database) then a zero is stored in register P2. If AUTOVACUUM is disabled then a zero is stored in register P2.

See also: Clear

Divide | Divide the value in register P1 by the value in register P2 and store the result in register P3 (P3=P2/P1). If the value in register P1 is zero, then the result is NULL. If either input is NULL, the result is NULL.
DropIndex | Remove the internal (in-memory) data structures that describe the index named P4 in database P1. This is called after an index is dropped from disk (using the Destroy opcode) in order to keep the internal representation of the schema consistent with what is on disk.
DropTable | Remove the internal (in-memory) data structures that describe the table named P4 in database P1. This is called after a table is dropped from disk (using the Destroy opcode) in order to keep the internal representation of the schema consistent with what is on disk.
DropTrigger | Remove the internal (in-memory) data structures that describe the trigger named P4 in database P1. This is called after a trigger is dropped from disk (using the Destroy opcode) in order to keep the internal representation of the schema consistent with what is on disk.
EndCoroutine | The instruction at the address in register P1 is a Yield. Jump to the P2 parameter of that Yield. After the jump, register P1 becomes undefined. See also: InitCoroutine

Eq

This works just like the Lt opcode except that the jump is taken if the operands in registers P1 and P3 are equal. See the Lt opcode for additional information.

If SQLITE_NULLEQ is set in P5 then the result of comparison is always either true or false and is never NULL. If both operands are NULL then the result of comparison is true. If either operand is NULL then the result is false. If neither operand is NULL the result is the same as it would be if the SQLITE_NULLEQ flag were omitted from P5.

Expire | Cause precompiled statements to expire. When an expired statement is executed using sqlite3_step() it will either automatically reprepare itself (if it was originally created using sqlite3_prepare_v2()) or it will fail with SQLITE_SCHEMA. If P1 is 0, then all SQL statements become expired. If P1 is non-zero, then only the currently executing statement is expired.
FkCounter | Increment a "constraint counter" by P2 (P2 may be negative or positive). If P1 is non-zero, the database constraint counter is incremented (deferred foreign key constraints). Otherwise, if P1 is zero, the statement counter is incremented (immediate foreign key constraints).

FkIfZero

This opcode tests if a foreign key constraint-counter is currently zero. If so, jump to instruction P2. Otherwise, fall through to the next instruction.

If P1 is non-zero, then the jump is taken if the database constraint-counter is zero (the one that counts deferred constraint violations). If P1 is zero, the jump is taken if the statement constraint-counter is zero (immediate foreign key constraint violations).

Found

If P4==0 then register P3 holds a blob constructed by MakeRecord. If P4>0 then register P3 is the first of P4 registers that form an unpacked record.

Cursor P1 is on an index btree. If the record identified by P3 and P4 is a prefix of any entry in P1 then a jump is made to P2 and P1 is left pointing at the matching entry.

This operation leaves the cursor in a state where it can be advanced in the forward direction. The Next instruction will work, but not the Prev instruction.

See also: NotFound, NoConflict, NotExists. SeekGe

Function

Invoke a user function (P4 is a pointer to a Function structure that defines the function) with P5 arguments taken from register P2 and successors. The result of the function is stored in register P3. Register P3 must not be one of the function inputs.

P1 is a 32-bit bitmask indicating whether or not each argument to the function was determined to be constant at compile time. If the first argument was constant then bit 0 of P1 is set. This is used to determine whether meta data associated with a user function argument using the sqlite3_set_auxdata() API may be safely retained until the next invocation of this opcode.

See also: AggStep and AggFinal

Ge | This works just like the Lt opcode except that the jump is taken if the content of register P3 is greater than or equal to the content of register P1. See the Lt opcode for additional information.
Gosub | Write the current address onto register P1 and then jump to address P2.

Goto

An unconditional jump to address P2. The next instruction executed will be the one at index P2 from the beginning of the program.

The P1 parameter is not actually used by this opcode. However, it is sometimes set to 1 instead of 0 as a hint to the command-line shell that this Goto is the bottom of a loop and that the lines from P2 down to the current line should be indented for EXPLAIN output.

Gt | This works just like the Lt opcode except that the jump is taken if the content of register P3 is greater than the content of register P1. See the Lt opcode for additional information.

Halt

Exit immediately. All open cursors, etc are closed automatically.

P1 is the result code returned by sqlite3_exec(), sqlite3_reset(), or sqlite3_finalize(). For a normal halt, this should be SQLITE_OK (0). For errors, it can be some other value. If P1!=0 then P2 will determine whether or not to rollback the current transaction. Do not rollback if P2==OE_Fail. Do the rollback if P2==OE_Rollback. If P2==OE_Abort, then back out all changes that have occurred during this execution of the VDBE, but do not rollback the transaction.

If P4 is not null then it is an error message string.

P5 is a value between 0 and 4, inclusive, that modifies the P4 string.

0: (no change) 1: NOT NULL contraint failed: P4 2: UNIQUE constraint failed: P4 3: CHECK constraint failed: P4 4: FOREIGN KEY constraint failed: P4

If P5 is not zero and P4 is NULL, then everything after the ":" is omitted.

There is an implied "Halt 0 0 0" instruction inserted at the very end of every program. So a jump past the last instruction of the program is the same as executing Halt.

HaltIfNull | Check the value in register P3. If it is NULL then Halt using parameter P1, P2, and P4 as if this were a Halt instruction. If the value in register P3 is not NULL, then this routine is a no-op. The P5 parameter should be 1.
IdxDelete | The content of P3 registers starting at register P2 form an unpacked index key. This opcode removes that entry from the index opened by cursor P1.
IdxGE | The P4 register values beginning with P3 form an unpacked index key that omits the PRIMARY KEY. Compare this key value against the index that P1 is currently pointing to, ignoring the PRIMARY KEY or ROWID fields at the end. If the P1 index entry is greater than or equal to the key value then jump to P2. Otherwise fall through to the next instruction.
IdxGT | The P4 register values beginning with P3 form an unpacked index key that omits the PRIMARY KEY. Compare this key value against the index that P1 is currently pointing to, ignoring the PRIMARY KEY or ROWID fields at the end. If the P1 index entry is greater than the key value then jump to P2. Otherwise fall through to the next instruction.

IdxInsert

Register P2 holds an SQL index key made using the MakeRecord instructions. This opcode writes that key into the index P1. Data for the entry is nil.

P3 is a flag that provides a hint to the b-tree layer that this insert is likely to be an append.

If P5 has the OPFLAG_NCHANGE bit set, then the change counter is incremented by this instruction. If the OPFLAG_NCHANGE bit is clear, then the change counter is unchanged.

If P5 has the OPFLAG_USESEEKRESULT bit set, then the cursor must have just done a seek to the spot where the new entry is to be inserted. This flag avoids doing an extra seek.

This instruction only works for indices. The equivalent instruction for tables is Insert.

IdxLE | The P4 register values beginning with P3 form an unpacked index key that omits the PRIMARY KEY or ROWID. Compare this key value against the index that P1 is currently pointing to, ignoring the PRIMARY KEY or ROWID on the P1 index. If the P1 index entry is less than or equal to the key value then jump to P2. Otherwise fall through to the next instruction.
IdxLT | The P4 register values beginning with P3 form an unpacked index key that omits the PRIMARY KEY or ROWID. Compare this key value against the index that P1 is currently pointing to, ignoring the PRIMARY KEY or ROWID on the P1 index. If the P1 index entry is less than the key value then jump to P2. Otherwise fall through to the next instruction.
IdxRowid | Write into register P2 an integer which is the last entry in the record at the end of the index key pointed to by cursor P1. This integer should be the rowid of the table entry to which this index entry points. See also: Rowid, MakeRecord.
If | Jump to P2 if the value in register P1 is true. The value is considered true if it is numeric and non-zero. If the value in P1 is NULL then take the jump if and only if P3 is non-zero.
IfNeg | Register P1 must contain an integer. Add literal P3 to the value in register P1 then if the value of register P1 is less than zero, jump to P2.
IfNot | Jump to P2 if the value in register P1 is False. The value is considered false if it has a numeric value of zero. If the value in P1 is NULL then take the jump if and only if P3 is non-zero.
IfPos | If the value of register P1 is 1 or greater, jump to P2. It is illegal to use this instruction on a register that does not contain an integer. An assertion fault will result if you try.
IfZero | The register P1 must contain an integer. Add literal P3 to the value in register P1. If the result is exactly 0, jump to P2.
IncrVacuum | Perform a single step of the incremental vacuum procedure on the P1 database. If the vacuum has finished, jump to instruction P2. Otherwise, fall through to the next instruction.
Init | Programs contain a single instance of this opcode as the very first opcode. If tracing is enabled (by the sqlite3_trace()) interface, then the UTF-8 string contained in P4 is emitted on the trace callback. Or if P4 is blank, use the string returned by sqlite3_sql(). If P2 is not zero, jump to instruction P2.
InitCoroutine | Set up register P1 so that it will Yield to the coroutine located at address P3. If P2!=0 then the coroutine implementation immediately follows this opcode. So jump over the coroutine implementation to address P2. See also: EndCoroutine

Insert

Write an entry into the table of cursor P1. A new entry is created if it doesn't already exist or the data for an existing entry is overwritten. The data is the value MEM_Blob stored in register number P2. The key is stored in register P3. The key must be a MEM_Int.

If the OPFLAG_NCHANGE flag of P5 is set, then the row change count is incremented (otherwise not). If the OPFLAG_LASTROWID flag of P5 is set, then rowid is stored for subsequent return by the sqlite3_last_insert_rowid() function (otherwise it is unmodified).

If the OPFLAG_USESEEKRESULT flag of P5 is set and if the result of the last seek operation (OP_NotExists) was a success, then this operation will not attempt to find the appropriate row before doing the insert but will instead overwrite the row that the cursor is currently pointing to. Presumably, the prior NotExists opcode has already positioned the cursor correctly. This is an optimization that boosts performance by avoiding redundant seeks.

If the OPFLAG_ISUPDATE flag is set, then this opcode is part of an UPDATE operation. Otherwise (if the flag is clear) then this opcode is part of an INSERT operation. The difference is only important to the update hook.

Parameter P4 may point to a string containing the table-name, or may be NULL. If it is not NULL, then the update-hook (sqlite3.xUpdateCallback) is invoked following a successful insert.

(WARNING/TODO: If P1 is a pseudo-cursor and P2 is dynamically allocated, then ownership of P2 is transferred to the pseudo-cursor and register P2 becomes ephemeral. If the cursor is changed, the value of register P2 will then change. Make sure this does not cause any problems.)

This instruction only works on tables. The equivalent instruction for indices is IdxInsert.

InsertInt | This works exactly like Insert except that the key is the integer value P3, not the value of the integer stored in register P3.
Int64 | P4 is a pointer to a 64-bit integer value. Write that value into register P2.
Integer | The 32-bit integer value P1 is written into register P2.

IntegrityCk

Do an analysis of the currently open database. Store in register P1 the text of an error message describing any problems. If no problems are found, store a NULL in register P1.

The register P3 contains the maximum number of allowed errors. At most reg(P3) errors will be reported. In other words, the analysis stops as soon as reg(P1) errors are seen. Reg(P1) is updated with the number of errors remaining.

The root page numbers of all tables in the database are integer stored in reg(P1), reg(P1+1), reg(P1+2), .... There are P2 tables total.

If P5 is not zero, the check is done on the auxiliary database file, not the main database file.

This opcode is used to implement the integrity_check pragma.

IsNull | Jump to P2 if the value in register P1 is NULL.
JournalMode | Change the journal mode of database P1 to P3. P3 must be one of the PAGER_JOURNALMODE_XXX values. If changing between the various rollback modes (delete, truncate, persist, off and memory), this is a simple operation. No IO is required. If changing into or out of WAL mode the procedure is more complicated. Write a string containing the final journal-mode to register P2.
Jump | Jump to the instruction at address P1, P2, or P3 depending on whether in the most recent Compare instruction the P1 vector was less than equal to, or greater than the P2 vector, respectively.

Last

The next use of the Rowid or Column or Prev instruction for P1 will refer to the last entry in the database table or index. If the table or index is empty and P2>0, then jump immediately to P2. If P2 is 0 or if the table or index is not empty, fall through to the following instruction.

This opcode leaves the cursor configured to move in reverse order, from the end toward the beginning. In other words, the cursor is configured to use Prev, not Next.

Le | This works just like the Lt opcode except that the jump is taken if the content of register P3 is less than or equal to the content of register P1. See the Lt opcode for additional information.
LoadAnalysis | Read the sqlite_stat1 table for database P1 and load the content of that table into the internal index hash table. This will cause the analysis to be used when preparing all subsequent queries.

Lt

Compare the values in register P1 and P3. If reg(P3)<reg(P1) then jump to address P2.

If the SQLITE_JUMPIFNULL bit of P5 is set and either reg(P1) or reg(P3) is NULL then take the jump. If the SQLITE_JUMPIFNULL bit is clear then fall through if either operand is NULL.

The SQLITE_AFF_MASK portion of P5 must be an affinity character - SQLITE_AFF_TEXT, SQLITE_AFF_INTEGER, and so forth. An attempt is made to coerce both inputs according to this affinity before the comparison is made. If the SQLITE_AFF_MASK is 0x00, then numeric affinity is used. Note that the affinity conversions are stored back into the input registers P1 and P3. So this opcode can cause persistent changes to registers P1 and P3.

Once any conversions have taken place, and neither value is NULL, the values are compared. If both values are blobs then memcmp() is used to determine the results of the comparison. If both values are text, then the appropriate collating function specified in P4 is used to do the comparison. If P4 is not specified then memcmp() is used to compare text string. If both values are numeric, then a numeric comparison is used. If the two values are of different types, then numbers are considered less than strings and strings are considered less than blobs.

If the SQLITE_STOREP2 bit of P5 is set, then do not jump. Instead, store a boolean result (either 0, or 1, or NULL) in register P2.

If the SQLITE_NULLEQ bit is set in P5, then NULL values are considered equal to one another, provided that they do not have their MEM_Cleared bit set.

MakeRecord

Convert P2 registers beginning with P1 into the record format use as a data record in a database table or as a key in an index. The Column opcode can decode the record later.

P4 may be a string that is P2 characters long. The nth character of the string indicates the column affinity that should be used for the nth field of the index key.

The mapping from character to affinity is given by the SQLITE_AFF_ macros defined in sqliteInt.h.

If P4 is NULL then all index fields have the affinity NONE.

MaxPgcnt | Try to set the maximum page count for database P1 to the value in P3. Do not let the maximum page count fall below the current page count and do not change the maximum page count value if P3==0. Store the maximum page count after the change in register P2.
MemMax | P1 is a register in the root frame of this VM (the root frame is different from the current frame if this instruction is being executed within a sub-program). Set the value of register P1 to the maximum of its current value and the value in register P2. This instruction throws an error if the memory cell is not initially an integer.
Move | Move the P3 values in register P1..P1+P3-1 over into registers P2..P2+P3-1. Registers P1..P1+P3-1 are left holding a NULL. It is an error for register ranges P1..P1+P3-1 and P2..P2+P3-1 to overlap. It is an error for P3 to be less than 1.
Multiply | Multiply the value in register P1 by the value in register P2 and store the result in register P3. If either input is NULL, the result is NULL.
MustBeInt | Force the value in register P1 to be an integer. If the value in P1 is not an integer and cannot be converted into an integer without data loss, then jump immediately to P2, or if P2==0 raise an SQLITE_MISMATCH exception.

Ne

This works just like the Lt opcode except that the jump is taken if the operands in registers P1 and P3 are not equal. See the Lt opcode for additional information.

If SQLITE_NULLEQ is set in P5 then the result of comparison is always either true or false and is never NULL. If both operands are NULL then the result of comparison is false. If either operand is NULL then the result is true. If neither operand is NULL the result is the same as it would be if the SQLITE_NULLEQ flag were omitted from P5.

NewRowid

Get a new integer record number (a.k.a "rowid") used as the key to a table. The record number is not previously used as a key in the database table that cursor P1 points to. The new record number is written written to register P2.

If P3>0 then P3 is a register in the root frame of this VDBE that holds the largest previously generated record number. No new record numbers are allowed to be less than this value. When this value reaches its maximum, an SQLITE_FULL error is generated. The P3 register is updated with the ' generated record number. This P3 mechanism is used to help implement the AUTOINCREMENT feature.

Next

Advance cursor P1 so that it points to the next key/data pair in its table or index. If there are no more key/value pairs then fall through to the following instruction. But if the cursor advance was successful, jump immediately to P2.

The Next opcode is only valid following an SeekGT, SeekGE, or Rewind opcode used to position the cursor. Next is not allowed to follow SeekLT, SeekLE, or Last.

The P1 cursor must be for a real table, not a pseudo-table. P1 must have been opened prior to this opcode or the program will segfault.

The P3 value is a hint to the btree implementation. If P3==1, that means P1 is an SQL index and that this instruction could have been omitted if that index had been unique. P3 is usually 0. P3 is always either 0 or 1.

P4 is always of type P4_ADVANCE. The function pointer points to sqlite3BtreeNext().

If P5 is positive and the jump is taken, then event counter number P5-1 in the prepared statement is incremented.

See also: Prev, NextIfOpen

NextIfOpen | This opcode works just like Next except that if cursor P1 is not open it behaves a no-op.

NoConflict

If P4==0 then register P3 holds a blob constructed by MakeRecord. If P4>0 then register P3 is the first of P4 registers that form an unpacked record.

Cursor P1 is on an index btree. If the record identified by P3 and P4 contains any NULL value, jump immediately to P2. If all terms of the record are not-NULL then a check is done to determine if any row in the P1 index btree has a matching key prefix. If there are no matches, jump immediately to P2. If there is a match, fall through and leave the P1 cursor pointing to the matching row.

This opcode is similar to NotFound with the exceptions that the branch is always taken if any part of the search key input is NULL.

This operation leaves the cursor in a state where it cannot be advanced in either direction. In other words, the Next and Prev opcodes do not work after this operation.

See also: NotFound, Found, NotExists

Noop | Do nothing. This instruction is often useful as a jump destination.
Not | Interpret the value in register P1 as a boolean value. Store the boolean complement in register P2. If the value in register P1 is NULL, then a NULL is stored in P2.

NotExists

P1 is the index of a cursor open on an SQL table btree (with integer keys). P3 is an integer rowid. If P1 does not contain a record with rowid P3 then jump immediately to P2. If P1 does contain a record with rowid P3 then leave the cursor pointing at that record and fall through to the next instruction.

The NotFound opcode performs the same operation on index btrees (with arbitrary multi-value keys).

This opcode leaves the cursor in a state where it cannot be advanced in either direction. In other words, the Next and Prev opcodes will not work following this opcode.

See also: Found, NotFound, NoConflict

NotFound

If P4==0 then register P3 holds a blob constructed by MakeRecord. If P4>0 then register P3 is the first of P4 registers that form an unpacked record.

Cursor P1 is on an index btree. If the record identified by P3 and P4 is not the prefix of any entry in P1 then a jump is made to P2. If P1 does contain an entry whose prefix matches the P3/P4 record then control falls through to the next instruction and P1 is left pointing at the matching entry.

This operation leaves the cursor in a state where it cannot be advanced in either direction. In other words, the Next and Prev opcodes do not work after this operation.

See also: Found, NotExists, NoConflict

NotNull | Jump to P2 if the value in register P1 is not NULL.
Null | Write a NULL into registers P2. If P3 greater than P2, then also write NULL into register P3 and every register in between P2 and P3. If P3 is less than P2 (typically P3 is zero) then only register P2 is set to NULL. If the P1 value is non-zero, then also set the MEM_Cleared flag so that NULL values will not compare equal even if SQLITE_NULLEQ is set on Ne or Eq.
NullRow | Move the cursor P1 to a null row. Any Column operations that occur while the cursor is on the null row will always write a NULL.
Once | Check the "once" flag number P1. If it is set, jump to instruction P2. Otherwise, set the flag and fall through to the next instruction. In other words, this opcode causes all following opcodes up through P2 (but not including P2) to run just once and to be skipped on subsequent times through the loop. All "once" flags are initially cleared whenever a prepared statement first begins to run.
OpenAutoindex | This opcode works the same as OpenEphemeral. It has a different name to distinguish its use. Tables created using by this opcode will be used for automatically created transient indices in joins.

OpenEphemeral

Open a new cursor P1 to a transient table. The cursor is always opened read/write even if the main database is read-only. The ephemeral table is deleted automatically when the cursor is closed.

P2 is the number of columns in the ephemeral table. The cursor points to a BTree table if P4==0 and to a BTree index if P4 is not 0. If P4 is not NULL, it points to a KeyInfo structure that defines the format of keys in the index.

The P5 parameter can be a mask of the BTREE_* flags defined in btree.h. These flags control aspects of the operation of the btree. The BTREE_OMIT_JOURNAL and BTREE_SINGLE flags are added automatically.

OpenPseudo

Open a new cursor that points to a fake table that contains a single row of data. The content of that one row is the content of memory register P2. In other words, cursor P1 becomes an alias for the MEM_Blob content contained in register P2.

A pseudo-table created by this opcode is used to hold a single row output from the sorter so that the row can be decomposed into individual columns using the Column opcode. The Column opcode is the only cursor opcode that works with a pseudo-table.

P3 is the number of fields in the records that will be stored by the pseudo-table.

OpenRead

Open a read-only cursor for the database table whose root page is P2 in a database file. The database file is determined by P3. P3==0 means the main database, P3==1 means the database used for temporary tables, and P3>1 means used the corresponding attached database. Give the new cursor an identifier of P1. The P1 values need not be contiguous but all P1 values should be small integers. It is an error for P1 to be negative.

If P5!=0 then use the content of register P2 as the root page, not the value of P2 itself.

There will be a read lock on the database whenever there is an open cursor. If the database was unlocked prior to this instruction then a read lock is acquired as part of this instruction. A read lock allows other processes to read the database but prohibits any other process from modifying the database. The read lock is released when all cursors are closed. If this instruction attempts to get a read lock but fails, the script terminates with an SQLITE_BUSY error code.

The P4 value may be either an integer (P4_INT32) or a pointer to a KeyInfo structure (P4_KEYINFO). If it is a pointer to a KeyInfo structure, then said structure defines the content and collating sequence of the index being opened. Otherwise, if P4 is an integer value, it is set to the number of columns in the table.

See also: OpenWrite, ReopenIdx

OpenWrite

Open a read/write cursor named P1 on the table or index whose root page is P2. Or if P5!=0 use the content of register P2 to find the root page.

The P4 value may be either an integer (P4_INT32) or a pointer to a KeyInfo structure (P4_KEYINFO). If it is a pointer to a KeyInfo structure, then said structure defines the content and collating sequence of the index being opened. Otherwise, if P4 is an integer value, it is set to the number of columns in the table, or to the largest index of any column of the table that is actually used.

This instruction works just like OpenRead except that it opens the cursor in read/write mode. For a given table, there can be one or more read-only cursors or a single read/write cursor but not both.

See also OpenRead.

Or | Take the logical OR of the values in register P1 and P2 and store the answer in register P3. If either P1 or P2 is nonzero (true) then the result is 1 (true) even if the other input is NULL. A NULL and false or two NULLs give a NULL output.
Pagecount | Write the current number of pages in database P1 to memory cell P2.

Param

This opcode is only ever present in sub-programs called via the Program instruction. Copy a value currently stored in a memory cell of the calling (parent) frame to cell P2 in the current frames address space. This is used by trigger programs to access the new.* and old.* values.

The address of the cell in the parent frame is determined by adding the value of the P1 argument to the value of the P1 argument to the calling Program instruction.

ParseSchema | Read and parse all entries from the SQLITE_MASTER table of database P1 that match the WHERE clause P4. This opcode invokes the parser to create a new virtual machine, then runs the new virtual machine. It is thus a re-entrant opcode.
Permutation | Set the permutation used by the Compare operator to be the array of integers in P4. The permutation is only valid until the next Compare that has the OPFLAG_PERMUTE bit set in P5. Typically the Permutation should occur immediately prior to the Compare.

Prev

Back up cursor P1 so that it points to the previous key/data pair in its table or index. If there is no previous key/value pairs then fall through to the following instruction. But if the cursor backup was successful, jump immediately to P2.

The Prev opcode is only valid following an SeekLT, SeekLE, or Last opcode used to position the cursor. Prev is not allowed to follow SeekGT, SeekGE, or Rewind.

The P1 cursor must be for a real table, not a pseudo-table. If P1 is not open then the behavior is undefined.

The P3 value is a hint to the btree implementation. If P3==1, that means P1 is an SQL index and that this instruction could have been omitted if that index had been unique. P3 is usually 0. P3 is always either 0 or 1.

P4 is always of type P4_ADVANCE. The function pointer points to sqlite3BtreePrevious().

If P5 is positive and the jump is taken, then event counter number P5-1 in the prepared statement is incremented.

PrevIfOpen | This opcode works just like Prev except that if cursor P1 is not open it behaves a no-op.

Program

Execute the trigger program passed as P4 (type P4_SUBPROGRAM).

P1 contains the address of the memory cell that contains the first memory cell in an array of values used as arguments to the sub-program. P2 contains the address to jump to if the sub-program throws an IGNORE exception using the RAISE() function. Register P3 contains the address of a memory cell in this (the parent) VM that is used to allocate the memory required by the sub-vdbe at runtime.

P4 is a pointer to the VM containing the trigger program.

If P5 is non-zero, then recursive program invocation is enabled.

ReadCookie

Read cookie number P3 from database P1 and write it into register P2. P3==1 is the schema version. P3==2 is the database format. P3==3 is the recommended pager cache size, and so forth. P1==0 is the main database file and P1==1 is the database file used to store temporary tables.

There must be a read-lock on the database (either a transaction must be started or there must be an open cursor) before executing this instruction.

Real | P4 is a pointer to a 64-bit floating point value. Write that value into register P2.
RealAffinity | If register P1 holds an integer convert it to a real value. This opcode is used when extracting information from a column that has REAL affinity. Such column values may still be stored as integers, for space efficiency, but after extraction we want them to have only a real value.
Remainder | Compute the remainder after integer register P2 is divided by register P1 and store the result in register P3. If the value in register P1 is zero the result is NULL. If either operand is NULL, the result is NULL.

ReopenIdx

The ReopenIdx opcode works exactly like ReadOpen except that it first checks to see if the cursor on P1 is already open with a root page number of P2 and if it is this opcode becomes a no-op. In other words, if the cursor is already open, do not reopen it.

The ReopenIdx opcode may only be used with P5==0 and with P4 being a P4_KEYINFO object. Furthermore, the P3 value must be the same as every other ReopenIdx or OpenRead for the same cursor number.

See the OpenRead opcode documentation for additional information.

ResetCount | The value of the change counter is copied to the database handle change counter (returned by subsequent calls to sqlite3_changes()). Then the VMs internal change counter resets to 0. This is used by trigger programs.
ResetSorter | Delete all contents from the ephemeral table or sorter that is open on cursor P1. This opcode only works for cursors used for sorting and opened with OpenEphemeral or SorterOpen.
ResultRow | The registers P1 through P1+P2-1 contain a single row of results. This opcode causes the sqlite3_step() call to terminate with an SQLITE_ROW return code and it sets up the sqlite3_stmt structure to provide access to the r(P1)..r(P1+P2-1) values as the result row.
Return | Jump to the next instruction after the address in register P1. After the jump, register P1 becomes undefined.

Rewind

The next use of the Rowid or Column or Next instruction for P1 will refer to the first entry in the database table or index. If the table or index is empty and P2>0, then jump immediately to P2. If P2 is 0 or if the table or index is not empty, fall through to the following instruction.

This opcode leaves the cursor configured to move in forward order, from the beginning toward the end. In other words, the cursor is configured to use Next, not Prev.

RowData | Write into register P2 the complete row data for cursor P1. There is no interpretation of the data. It is just copied onto the P2 register exactly as it is found in the database file. If the P1 cursor must be pointing to a valid row (not a NULL row) of a real table, not a pseudo-table.
Rowid | Store in register P2 an integer which is the key of the table entry that P1 is currently point to. P1 can be either an ordinary table or a virtual table. There used to be a separate OP_VRowid opcode for use with virtual tables, but this one opcode now works for both table types.
RowKey | Write into register P2 the complete row key for cursor P1. There is no interpretation of the data. The key is copied onto the P2 register exactly as it is found in the database file. If the P1 cursor must be pointing to a valid row (not a NULL row) of a real table, not a pseudo-table.
RowSetAdd | Insert the integer value held by register P2 into a boolean index held in register P1. An assertion fails if P2 is not an integer.
RowSetRead | Extract the smallest value from boolean index P1 and put that value into register P3. Or, if boolean index P1 is initially empty, leave P3 unchanged and jump to instruction P2.

RowSetTest

Register P3 is assumed to hold a 64-bit integer value. If register P1 contains a RowSet object and that RowSet object contains the value held in P3, jump to register P2. Otherwise, insert the integer in P3 into the RowSet and continue on to the next opcode.

The RowSet object is optimized for the case where successive sets of integers, where each set contains no duplicates. Each set of values is identified by a unique P4 value. The first set must have P4==0, the final set P4=-1. P4 must be either -1 or non-negative. For non-negative values of P4 only the lower 4 bits are significant.

This allows optimizations: (a) when P4==0 there is no need to test the rowset object for P3, as it is guaranteed not to contain it, (b) when P4==-1 there is no need to insert the value, as it will never be tested for, and (c) when a value that is part of set X is inserted, there is no need to search to see if the same value was previously inserted as part of set X (only if it was previously inserted as part of some other set).

Savepoint | Open, release or rollback the savepoint named by parameter P4, depending on the value of P1. To open a new savepoint, P1==0. To release (commit) an existing savepoint, P1==1, or to rollback an existing savepoint P1==2.

SCopy

Make a shallow copy of register P1 into register P2.

This instruction makes a shallow copy of the value. If the value is a string or blob, then the copy is only a pointer to the original and hence if the original changes so will the copy. Worse, if the original is deallocated, the copy becomes invalid. Thus the program must guarantee that the original will not change during the lifetime of the copy. Use Copy to make a complete copy.

Seek | P1 is an open table cursor and P2 is a rowid integer. Arrange for P1 to move so that it points to the rowid given by P2. This is actually a deferred seek. Nothing actually happens until the cursor is used to read a record. That way, if no reads occur, no unnecessary I/O happens.

SeekGE

If cursor P1 refers to an SQL table (B-Tree that uses integer keys), use the value in register P3 as the key. If cursor P1 refers to an SQL index, then P3 is the first in an array of P4 registers that are used as an unpacked index key.

Reposition cursor P1 so that it points to the smallest entry that is greater than or equal to the key value. If there are no records greater than or equal to the key and P2 is not zero, then jump to P2.

This opcode leaves the cursor configured to move in forward order, from the beginning toward the end. In other words, the cursor is configured to use Next, not Prev.

See also: Found, NotFound, SeekLt, SeekGt, SeekLe

SeekGT

If cursor P1 refers to an SQL table (B-Tree that uses integer keys), use the value in register P3 as a key. If cursor P1 refers to an SQL index, then P3 is the first in an array of P4 registers that are used as an unpacked index key.

Reposition cursor P1 so that it points to the smallest entry that is greater than the key value. If there are no records greater than the key and P2 is not zero, then jump to P2.

This opcode leaves the cursor configured to move in forward order, from the beginning toward the end. In other words, the cursor is configured to use Next, not Prev.

See also: Found, NotFound, SeekLt, SeekGe, SeekLe

SeekLE

If cursor P1 refers to an SQL table (B-Tree that uses integer keys), use the value in register P3 as a key. If cursor P1 refers to an SQL index, then P3 is the first in an array of P4 registers that are used as an unpacked index key.

Reposition cursor P1 so that it points to the largest entry that is less than or equal to the key value. If there are no records less than or equal to the key and P2 is not zero, then jump to P2.

This opcode leaves the cursor configured to move in reverse order, from the end toward the beginning. In other words, the cursor is configured to use Prev, not Next.

See also: Found, NotFound, SeekGt, SeekGe, SeekLt

SeekLT

If cursor P1 refers to an SQL table (B-Tree that uses integer keys), use the value in register P3 as a key. If cursor P1 refers to an SQL index, then P3 is the first in an array of P4 registers that are used as an unpacked index key.

Reposition cursor P1 so that it points to the largest entry that is less than the key value. If there are no records less than the key and P2 is not zero, then jump to P2.

This opcode leaves the cursor configured to move in reverse order, from the end toward the beginning. In other words, the cursor is configured to use Prev, not Next.

See also: Found, NotFound, SeekGt, SeekGe, SeekLe

Sequence | Find the next available sequence number for cursor P1. Write the sequence number into register P2. The sequence number on the cursor is incremented after this instruction.
SequenceTest | P1 is a sorter cursor. If the sequence counter is currently zero, jump to P2. Regardless of whether or not the jump is taken, increment the the sequence value.
SetCookie | Write the content of register P3 (interpreted as an integer) into cookie number P2 of database P1. P2==1 is the schema version. P2==2 is the database format. P2==3 is the recommended pager cache size, and so forth. P1==0 is the main database file and P1==1 is the database file used to store temporary tables. A transaction must be started before executing this opcode.
ShiftLeft | Shift the integer value in register P2 to the left by the number of bits specified by the integer in register P1. Store the result in register P3. If either input is NULL, the result is NULL.
ShiftRight | Shift the integer value in register P2 to the right by the number of bits specified by the integer in register P1. Store the result in register P3. If either input is NULL, the result is NULL.
SoftNull | Set register P1 to have the value NULL as seen by the MakeRecord instruction, but do not free any string or blob memory associated with the register, so that if the value was a string or blob that was previously copied using SCopy, the copies will continue to be valid.

Sort

This opcode does exactly the same thing as Rewind except that it increments an undocumented global variable used for testing.

Sorting is accomplished by writing records into a sorting index, then rewinding that index and playing it back from beginning to end. We use the Sort opcode instead of Rewind to do the rewinding so that the global variable will be incremented and regression tests can determine whether or not the optimizer is correctly optimizing out sorts.

SorterCompare

P1 is a sorter cursor. This instruction compares a prefix of the record blob in register P3 against a prefix of the entry that the sorter cursor currently points to. Only the first P4 fields of r[P3] and the sorter record are compared.

If either P3 or the sorter contains a NULL in one of their significant fields (not counting the P4 fields at the end which are ignored) then the comparison is assumed to be equal.

Fall through to next instruction if the two records compare equal to each other. Jump to P2 if they are different.

SorterData

Write into register P2 the current sorter data for sorter cursor P1. Then clear the column header cache on cursor P3.

This opcode is normally use to move a record out of the sorter and into a register that is the source for a pseudo-table cursor created using OpenPseudo. That pseudo-table cursor is the one that is identified by parameter P3. Clearing the P3 column cache as part of this opcode saves us from having to issue a separate NullRow instruction to clear that cache.

SorterOpen | This opcode works like OpenEphemeral except that it opens a transient index that is specifically designed to sort large tables using an external merge-sort algorithm. If argument P3 is non-zero, then it indicates that the sorter may assume that a stable sort considering the first P3 fields of each key is sufficient to produce the required results.
String | The string value P4 of length P1 (bytes) is stored in register P2.
String8 | P4 points to a nul terminated UTF-8 string. This opcode is transformed into a String before it is executed for the first time. During this transformation, the length of string P4 is computed and stored as the P1 parameter.
Subtract | Subtract the value in register P1 from the value in register P2 and store the result in register P3. If either input is NULL, the result is NULL.

TableLock

Obtain a lock on a particular table. This instruction is only used when the shared-cache feature is enabled.

P1 is the index of the database in sqlite3.aDb[] of the database on which the lock is acquired. A readlock is obtained if P3==0 or a write lock if P3==1.

P2 contains the root-page of the table to lock.

P4 contains a pointer to the name of the table being locked. This is only used to generate an error message if the lock cannot be obtained.

Transaction

Begin a transaction on database P1 if a transaction is not already active. If P2 is non-zero, then a write-transaction is started, or if a read-transaction is already active, it is upgraded to a write-transaction. If P2 is zero, then a read-transaction is started.

P1 is the index of the database file on which the transaction is started. Index 0 is the main database file and index 1 is the file used for temporary tables. Indices of 2 or more are used for attached databases.

If a write-transaction is started and the Vdbe.usesStmtJournal flag is true (this flag is set if the Vdbe may modify more than one row and may throw an ABORT exception), a statement transaction may also be opened. More specifically, a statement transaction is opened iff the database connection is currently not in autocommit mode, or if there are other active statements. A statement transaction allows the changes made by this VDBE to be rolled back after an error without having to roll back the entire transaction. If no error is encountered, the statement transaction will automatically commit when the VDBE halts.

If P5!=0 then this opcode also checks the schema cookie against P3 and the schema generation counter against P4. The cookie changes its value whenever the database schema changes. This operation is used to detect when that the cookie has changed and that the current process needs to reread the schema. If the schema cookie in P3 differs from the schema cookie in the database header or if the schema generation counter in P4 differs from the current generation counter, then an SQLITE_SCHEMA error is raised and execution halts. The sqlite3_step() wrapper function might then reprepare the statement and rerun it from the beginning.

Vacuum | Vacuum the entire database. This opcode will cause other virtual machines to be created and run. It may not be called from within a transaction.
Variable | Transfer the values of bound parameter P1 into register P2 If the parameter is named, then its name appears in P4. The P4 value is used by sqlite3_bind_parameter_name().
VBegin | P4 may be a pointer to an sqlite3_vtab structure. If so, call the xBegin method for that table. Also, whether or not P4 is set, check that this is not being called from within a callback to a virtual table xSync() method. If it is, the error code will be set to SQLITE_LOCKED.
VColumn | Store the value of the P2-th column of the row of the virtual-table that the P1 cursor is pointing to into register P3.
VCreate | P4 is the name of a virtual table in database P1. Call the xCreate method for that table.
VDestroy | P4 is the name of a virtual table in database P1. Call the xDestroy method of that table.

VFilter

P1 is a cursor opened using VOpen. P2 is an address to jump to if the filtered result set is empty.

P4 is either NULL or a string that was generated by the xBestIndex method of the module. The interpretation of the P4 string is left to the module implementation.

This opcode invokes the xFilter method on the virtual table specified by P1. The integer query plan parameter to xFilter is stored in register P3. Register P3+1 stores the argc parameter to be passed to the xFilter method. Registers P3+2..P3+1+argc are the argc additional parameters which are passed to xFilter as argv. Register P3+2 becomes argv[0] when passed to xFilter.

A jump is made to P2 if the result set after filtering would be empty.

VNext | Advance virtual table P1 to the next row in its result set and jump to instruction P2. Or, if the virtual table has reached the end of its result set, then fall through to the next instruction.
VOpen | P4 is a pointer to a virtual table object, an sqlite3_vtab structure. P1 is a cursor number. This opcode opens a cursor to the virtual table and stores that cursor in P1.
VRename | P4 is a pointer to a virtual table object, an sqlite3_vtab structure. This opcode invokes the corresponding xRename method. The value in register P1 is passed as the zName argument to the xRename method.

VUpdate

P4 is a pointer to a virtual table object, an sqlite3_vtab structure. This opcode invokes the corresponding xUpdate method. P2 values are contiguous memory cells starting at P3 to pass to the xUpdate invocation. The value in register (P3+P2-1) corresponds to the p2th element of the argv array passed to xUpdate.

The xUpdate method will do a DELETE or an INSERT or both. The argv[0] element (which corresponds to memory cell P3) is the rowid of a row to delete. If argv[0] is NULL then no deletion occurs. The argv[1] element is the rowid of the new row. This can be NULL to have the virtual table select the new rowid for itself. The subsequent elements in the array are the values of columns in the new row.

If P2==1 then no insert is performed. argv[0] is the rowid of a row to delete.

P1 is a boolean flag. If it is set to true and the xUpdate call is successful, then the value returned by sqlite3_last_insert_rowid() is set to the value of the rowid for the row just inserted.

P5 is the error actions (OE_Replace, OE_Fail, OE_Ignore, etc) to apply in the case of a constraint failure on an insert or update.

Yield | Swap the program counter with the value in register P1. This has the effect of yielding to a coroutine. If the coroutine that is launched by this instruction ends with Yield or Return then continue to the next instruction. But if the coroutine launched by this instruction ends with EndCoroutine, then jump to P2 rather than continuing with the next instruction. See also: InitCoroutine