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## SQLite Virtual Machine Opcodes

### 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. This document describes the operation of that virtual machine.

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 the document has not been updated.

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 three operands named P1, P2 and P3. P1 may be an arbitrary integer. P2 must be a non-negative integer. P2 is always the jump destination in any operation that might cause a jump. P3 is a null-terminated string or NULL. Some operators use all three 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 (1) a Halt instruction is seen, or (2) the program counter becomes one greater than the address of last instruction, or (3) 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 also contains an operand stack of unlimited depth. Many of the opcodes use operands from the stack. See the individual opcode descriptions for details.

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 (Open), 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 fixed memory locations with addresses beginning at zero and growing upward. Each memory location can hold an arbitrary string. The memory cells are typically used to hold the result of a scalar SELECT that is part of a larger expression.

The virtual machine contains a single sorter. The sorter is able to accumulate records, sort those records, then play the records back in sorted order. The sorter is used to implement the ORDER BY clause of a SELECT statement.

The virtual machine contains a single "List". The list stores a list of integers. The list is used to hold the rowids for records of a database table that needs to be modified. The WHERE clause of an UPDATE or DELETE statement scans through the table and writes the rowid of every record to be modified into the list. Then the list is played back and the table is modified in a separate step.

The virtual machine can contain an arbitrary number of "Sets". Each set holds an arbitrary number of strings. Sets are used to implement the IN operator with a constant right-hand side.

The virtual machine can open a single external file for reading. This external read file is used to implement the COPY command.

Finally, the virtual machine can have a single set of aggregators. An aggregator is a device used to implement the GROUP BY clause of a SELECT. An aggregator has one or more slots that can hold values being extracted by the select. The number of slots is the same for all aggregators and is defined by the AggReset operation. At any point in time a single aggregator is current or "has focus". There are operations to read or write to memory slots of the aggregator in focus. There are also operations to change the focus aggregator and to scan through all aggregators.

### 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.

You can use the sqlite command-line tool to see the instructions generated by an SQL statement. The following is an example:

> `$ sqlite ex1
> sqlite> .explain
> sqlite> explain delete from tbl1 where two<20;
> addr opcode p1 p2 p3
> ---- ------------ ----- ----- ----------------------------------------
> 0 Transaction 0 0
> 1 VerifyCookie 219 0
> 2 ListOpen 0 0
> 3 Open 0 3 tbl1
> 4 Rewind 0 0
> 5 Next 0 12
> 6 Column 0 1
> 7 Integer 20 0
> 8 Ge 0 5
> 9 Recno 0 0
> 10 ListWrite 0 0
> 11 Goto 0 5
> 12 Close 0 0
> 13 ListRewind 0 0
> 14 OpenWrite 0 3
> 15 ListRead 0 19
> 16 MoveTo 0 0
> 17 Delete 0 0
> 18 Goto 0 15
> 19 ListClose 0 0
> 20 Commit 0 0`

All you have to do is add the "EXPLAIN" keyword to the front of the SQL statement. But if you use the ".explain" command to sqlite first, it will set up the output mode to make the program more easily viewable.

If sqlite has been compiled without the "-DNDEBUG=1" option (that is, with the NDEBUG preprocessor macro not defined) then you can put the SQLite virtual machine in a mode where it will trace its execution by writing messages to standard output. The non-standard SQL "PRAGMA" comments can be used to turn tracing on and off. To turn tracing on, enter:

>     PRAGMA vdbe_trace=on;

You can turn tracing back off by entering a similar statement but changing the value "on" to "off".

### The Opcodes

There are currently 140 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.

Opcode Name | Description
--- | ---
AbsValue | Treat the top of the stack as a numeric quantity. Replace it with its absolute value. If the top of the stack is NULL its value is unchanged.
Add | Pop the top two elements from the stack, add them together, and push the result back onto the stack. If either element is a string then it is converted to a double using the atof() function before the addition. If either operand is NULL, the result is NULL.
AddImm | Add the value P1 to whatever is on top of the stack. The result is always an integer. To force the top of the stack to be an integer, just add 0.
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 P3 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 P3 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 P2 arguments. P3 is a pointer to the FuncDef structure that specifies the function. Use memory location P1 as the accumulator. The P2 arguments are popped from the stack.
And | Pop two values off the stack. Take the logical AND of the two values and push the resulting boolean value back onto the stack.
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 the COMMIT or ROLLBACK statement fails. This instruction causes the VM to halt.
BitAnd | Pop the top two elements from the stack. Convert both elements to integers. Push back onto the stack the bit-wise AND of the two elements. If either operand is NULL, the result is NULL.
BitNot | Interpret the top of the stack as an value. Replace it with its ones-complement. If the top of the stack is NULL its value is unchanged.
BitOr | Pop the top two elements from the stack. Convert both elements to integers. Push back onto the stack the bit-wise OR of the two elements. If either operand is NULL, the result is NULL.
Blob | P3 points to a blob of data P1 bytes long. Push this value onto the stack. This instruction is not coded directly by the compiler. Instead, the compiler layer specifies an OP_HexBlob opcode, with the hex string representation of the blob as P3. This opcode is transformed to an OP_Blob the first time it is executed.
Callback | The top P1 values on the stack represent a single result row from a query. 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 top P1 values as the result row. When the sqlite3_step() function is run again, the top P1 values will be automatically popped from the stack before the next instruction executes.
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. See also: Destroy
Close | Close a cursor previously opened as P1. If P1 is not currently open, this instruction is a no-op.
CollSeq | P3 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. 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.) Push onto the stack the value of the P2-th column contained in the data. If there are less that (P2+1) values in the record, push a NULL onto the stack. If the KeyAsData opcode has previously executed on this cursor, then the field might be extracted from the key rather than the data. If the column contains fewer than P2 fields, then push a NULL. Or if P3 is of type P3_MEM, then push the P3 value. The P3 value will be default value for a column that has been added using the ALTER TABLE ADD COLUMN command. If P3 is an ordinary string, just push a NULL. When P3 is a string it is really just a comment describing the value to be pushed, not a default value.
Concat | Look at the first P1+2 elements of the stack. Append them all together with the lowest element first. The original P1+2 elements are popped from the stack if P2==0 and retained if P2==1. If any element of the stack is NULL, then the result is NULL. When P1==1, this routine makes a copy of the top stack element into memory obtained from sqlite3_malloc().
ContextPop | Restore the Vdbe context to the state it was in when contextPush was last executed. The context stores the last insert row id, the last statement change count, and the current statement change count.
ContextPush | Save the current Vdbe context such that it can be restored by a ContextPop opcode. The context stores the last insert row id, the last statement change count, and the current statement change count.
CreateIndex | Allocate a new index in the main database file if P2==0 or in the auxiliary database file if P2==1. Push the page number of the root page of the new index onto the stack. See documentation on OP_CreateTable for additional information.
CreateTable | Allocate a new table in the main database file if P2==0 or in the auxiliary database file if P2==1. Push the page number for the root page of the new table onto the stack. 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 an Next loop. If the OPFLAG_NCHANGE flag of P2 is set, then the row change count is incremented (otherwise not). If P1 is a pseudo-table, then this instruction is a no-op.
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 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 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 pushed onto the stack. If no page movement was required (because the table being dropped was already the last one in the database) then a zero is pushed onto the stack. If AUTOVACUUM is disabled then a zero is pushed onto the stack. See also: Clear
Distinct | Use the top of the stack as a record created using MakeRecord. P1 is a cursor on a table that declared as an index. If that table contains an entry that matches the top of the stack fall thru. If the top of the stack matches no entry in P1 then jump to P2. The cursor is left pointing at the matching entry if it exists. The record on the top of the stack is not popped. This instruction is similar to NotFound except that this operation does not pop the key from the stack. The instruction is used to implement the DISTINCT operator on SELECT statements. The P1 table is not a true index but rather a record of all results that have produced so far. See also: Found, NotFound, MoveTo, IsUnique, NotExists
Divide | Pop the top two elements from the stack, divide the first (what was on top of the stack) from the second (the next on stack) and push the result back onto the stack. If either element is a string then it is converted to a double using the atof() function before the division. Division by zero returns NULL. If either operand is NULL, the result is NULL.
DropIndex | Remove the internal (in-memory) data structures that describe the index named P3 in database P1. This is called after an index is dropped 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 P3 in database P1. This is called after a table is dropped 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 P3 in database P1. This is called after a trigger is dropped in order to keep the internal representation of the schema consistent with what is on disk.
Dup | A copy of the P1-th element of the stack is made and pushed onto the top of the stack. The top of the stack is element 0. So the instruction "Dup 0 0 0" will make a copy of the top of the stack. If the content of the P1-th element is a dynamically allocated string, then a new copy of that string is made if P2==0. If P2!=0, then just a pointer to the string is copied. Also see the Pull instruction.
Eq | Pop the top two elements from the stack. If they are equal, then jump to instruction P2. Otherwise, continue to the next instruction. If the 0x100 bit of P1 is true and either operand is NULL then take the jump. If the 0x100 bit of P1 is clear then fall thru if either operand is NULL. If the 0x200 bit of P1 is set and either operand is NULL then both operands are converted to integers prior to comparison. NULL operands are converted to zero and non-NULL operands are converted to 1. Thus, for example, with 0x200 set, NULL==NULL is true whereas it would normally be NULL. Similarly, NULL==123 is false when 0x200 is set but is NULL when the 0x200 bit of P1 is clear. The least significant byte of P1 (mask 0xff) must be an affinity character - SQLITE_AFF_TEXT, SQLITE_AFF_INTEGER, and so forth. An attempt is made to coerce both values according to the affinity before the comparison is made. If the byte is 0x00, then numeric affinity is used. Once any conversions have taken place, and neither value is NULL, the values are compared. If both values are blobs, or both are text, then memcmp() is used to determine the results of the comparison. If both values are numeric, then a numeric comparison is used. If the two values are of different types, then they are inequal. If P2 is zero, do not jump. Instead, push an integer 1 onto the stack if the jump would have been taken, or a 0 if not. Push a NULL if either operand was NULL. If P3 is not NULL it is a pointer to a collating sequence (a CollSeq structure) that defines how to compare text.
Expire | Cause precompiled statements to become expired. An expired statement fails with an error code of SQLITE_SCHEMA if it is ever executed (via sqlite3_step()). If P1 is 0, then all SQL statements become expired. If P1 is non-zero, then only the currently executing statement is affected.
FifoRead | Attempt to read a single integer from the Fifo and push it onto the stack. If the Fifo is empty push nothing but instead jump to P2.
FifoWrite | Write the integer on the top of the stack into the Fifo.
ForceInt | Convert the top of the stack into an integer. If the current top of the stack is not numeric (meaning that is is a NULL or a string that does not look like an integer or floating point number) then pop the stack and jump to P2. If the top of the stack is numeric then convert it into the least integer that is greater than or equal to its current value if P1==0, or to the least integer that is strictly greater than its current value if P1==1.
Found | Top of the stack holds a blob constructed by MakeRecord. P1 is an index. If an entry that matches the top of the stack exists in P1 then jump to P2. If the top of the stack does not match any entry in P1 then fall thru. The P1 cursor is left pointing at the matching entry if it exists. The blob is popped off the top of the stack. This instruction is used to implement the IN operator where the left-hand side is a SELECT statement. P1 is not a true index but is instead a temporary index that holds the results of the SELECT statement. This instruction just checks to see if the left-hand side of the IN operator (stored on the top of the stack) exists in the result of the SELECT statement. See also: Distinct, NotFound, MoveTo, IsUnique, NotExists
Function | Invoke a user function (P3 is a pointer to a Function structure that defines the function) with P2 arguments taken from the stack. Pop all arguments from the stack and push back the result. 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 Eq opcode except that the jump is taken if the 2nd element down on the stack is greater than or equal to the top of the stack. See the Eq opcode for additional information.
Gosub | Push the current address plus 1 onto the return address stack and then jump to address P2. The return address stack is of limited depth. If too many OP_Gosub operations occur without intervening OP_Returns, then the return address stack will fill up and processing will abort with a fatal error.
Goto | An unconditional jump to address P2. The next instruction executed will be the one at index P2 from the beginning of the program.
Gt | This works just like the Eq opcode except that the jump is taken if the 2nd element down on the stack is greater than the top of the stack. See the Eq opcode for additional information.
Halt | Exit immediately. All open cursors, Fifos, 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 P3 is not null then it is an error message string. 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.
HexBlob | P3 is an UTF-8 SQL hex encoding of a blob. The blob is pushed onto the vdbe stack. The first time this instruction executes, in transforms itself into a 'Blob' opcode with a binary blob as P3.
IdxDelete | The top of the stack is an index key built using the either the MakeIdxRec or MakeRecord opcodes. This opcode removes that entry from the index.
IdxGE | The top of the stack is an index entry that omits the ROWID. Compare the top of stack against the index that P1 is currently pointing to. Ignore the ROWID on the P1 index. If the P1 index entry is greater than or equal to the top of the stack then jump to P2. Otherwise fall through to the next instruction. In either case, the stack is popped once. If P3 is the "+" string (or any other non-NULL string) then the index taken from the top of the stack is temporarily increased by an epsilon prior to the comparison. This make the opcode work like IdxGT except that if the key from the stack is a prefix of the key in the cursor, the result is false whereas it would be true with IdxGT.
IdxGT | The top of the stack is an index entry that omits the ROWID. Compare the top of stack against the index that P1 is currently pointing to. Ignore the ROWID on the P1 index. The top of the stack might have fewer columns that P1. If the P1 index entry is greater than the top of the stack then jump to P2. Otherwise fall through to the next instruction. In either case, the stack is popped once.
IdxInsert | The top of the stack holds a SQL index key made using either the MakeIdxRec or MakeRecord instructions. This opcode writes that key into the index P1. Data for the entry is nil. P2 is a flag that provides a hint to the b-tree layer that this insert is likely to be an append. This instruction only works for indices. The equivalent instruction for tables is OP_Insert.
IdxLT | The top of the stack is an index entry that omits the ROWID. Compare the top of stack against the index that P1 is currently pointing to. Ignore the ROWID on the P1 index. If the P1 index entry is less than the top of the stack then jump to P2. Otherwise fall through to the next instruction. In either case, the stack is popped once. If P3 is the "+" string (or any other non-NULL string) then the index taken from the top of the stack is temporarily increased by an epsilon prior to the comparison. This makes the opcode work like IdxLE.
IdxRowid | Push onto the stack 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, MakeIdxRec.
If | Pop a single boolean from the stack. If the boolean popped is true, then jump to p2. Otherwise continue to the next instruction. An integer is false if zero and true otherwise. A string is false if it has zero length and true otherwise. If the value popped of the stack is NULL, then take the jump if P1 is true and fall through if P1 is false.
IfMemNeg | If the value of memory cell P1 is less than zero, jump to P2. It is illegal to use this instruction on a memory cell that does not contain an integer. An assertion fault will result if you try.
IfMemPos | If the value of memory cell P1 is 1 or greater, jump to P2. It is illegal to use this instruction on a memory cell that does not contain an integer. An assertion fault will result if you try.
IfMemZero | If the value of memory cell P1 is exactly 0, jump to P2. It is illegal to use this instruction on a memory cell that does not contain an integer. An assertion fault will result if you try.
IfNot | Pop a single boolean from the stack. If the boolean popped is false, then jump to p2. Otherwise continue to the next instruction. An integer is false if zero and true otherwise. A string is false if it has zero length and true otherwise. If the value popped of the stack is NULL, then take the jump if P1 is true and fall through if P1 is false.
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.
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 on the top of the stack. The key is the next value down on the stack. The key must be an integer. The stack is popped twice by this instruction. If the OPFLAG_NCHANGE flag of P2 is set, then the row change count is incremented (otherwise not). If the OPFLAG_LASTROWID flag of P2 is set, then rowid is stored for subsequent return by the sqlite3_last_insert_rowid() function (otherwise it's unmodified). Parameter P3 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. This instruction only works on tables. The equivalent instruction for indices is OP_IdxInsert.
Int64 | P3 is a pointer to a 64-bit integer value. Push that value onto the stack.
Integer | The 32-bit integer value P1 is pushed onto the stack.
IntegrityCk | Do an analysis of the currently open database. Push onto the stack the text of an error message describing any problems. If no problems are found, push a NULL onto the stack. P1 is the address of a memory cell that contains the maximum number of allowed errors. At most mem[P1] errors will be reported. In other words, the analysis stops as soon as mem[P1] errors are seen. Mem[P1] is updated with the number of errors remaining. The root page numbers of all tables in the database are integer values on the stack. This opcode pulls as many integers as it can off of the stack and uses those numbers as the root pages. If P2 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 | Check the top of the stack and jump to P2 if the top of the stack is NULL. If P1 is positive, then pop P1 elements from the stack regardless of whether or not the jump is taken. If P1 is negative, pop -P1 elements from the stack only if the jump is taken and leave the stack unchanged if the jump is not taken.
IsUnique | The top of the stack is an integer record number. Call this record number R. The next on the stack is an index key created using MakeIdxRec. Call it K. This instruction pops R from the stack but it leaves K unchanged. P1 is an index. So it has no data and its key consists of a record generated by OP_MakeRecord where the last field is the rowid of the entry that the index refers to. This instruction asks if there is an entry in P1 where the fields matches K but the rowid is different from R. If there is no such entry, then there is an immediate jump to P2. If any entry does exist where the index string matches K but the record number is not R, then the record number for that entry is pushed onto the stack and control falls through to the next instruction. See also: Distinct, NotFound, NotExists, Found
Last | The next use of the Rowid or Column or Next 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.
Le | This works just like the Eq opcode except that the jump is taken if the 2nd element down on the stack is less than or equal to the top of the stack. See the Eq 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 | This works just like the Eq opcode except that the jump is taken if the 2nd element down on the stack is less than the top of the stack. See the Eq opcode for additional information.
MakeIdxRec | This opcode works just OP_MakeRecord except that it reads an extra integer from the stack (thus reading a total of abs(P1+1) entries) and appends that extra integer to the end of the record as a varint. This results in an index key.
MakeRecord | Convert the top abs(P1) entries of the stack into a single entry suitable for use as a data record in a database table or as a key in an index. The details of the format are irrelavant as long as the OP_Column opcode can decode the record later and as long as the sqlite3VdbeRecordCompare function will correctly compare two encoded records. Refer to source code comments for the details of the record format. The original stack entries are popped from the stack if P1>0 but remain on the stack if P1<0. If P2 is not zero and one or more of the entries are NULL, then jump to the address given by P2. This feature can be used to skip a uniqueness test on indices. P3 may be a string that is P1 characters long. The nth character of the string indicates the column affinity that should be used for the nth field of the index key (i.e. the first character of P3 corresponds to the lowest element on the stack). The mapping from character to affinity is given by the SQLITE_AFF_ macros defined in sqliteInt.h. If P3 is NULL then all index fields have the affinity NONE. See also OP_MakeIdxRec
MemIncr | Increment the integer valued memory cell P2 by the value in P1. It is illegal to use this instruction on a memory cell that does not contain an integer. An assertion fault will result if you try.
MemInt | Store the integer value P1 in memory cell P2.
MemLoad | Push a copy of the value in memory location P1 onto the stack. If the value is a string, then the value pushed is a pointer to the string that is stored in the memory location. If the memory location is subsequently changed (using OP_MemStore) then the value pushed onto the stack will change too.
MemMax | Set the value of memory cell P1 to the maximum of its current value and the value on the top of the stack. The stack is unchanged. This instruction throws an error if the memory cell is not initially an integer.
MemMove | Move the content of memory cell P2 over to memory cell P1. Any prior content of P1 is erased. Memory cell P2 is left containing a NULL.
MemNull | Store a NULL in memory cell P1
MemStore | Write the top of the stack into memory location P1. P1 should be a small integer since space is allocated for all memory locations between 0 and P1 inclusive. After the data is stored in the memory location, the stack is popped once if P2 is 1. If P2 is zero, then the original data remains on the stack.
MoveGe | Pop the top of the stack and use its value as a key. Reposition cursor P1 so that it points to the smallest entry that is greater than or equal to the key that was popped ffrom the stack. If there are no records greater than or equal to the key and P2 is not zero, then jump to P2. See also: Found, NotFound, Distinct, MoveLt, MoveGt, MoveLe
MoveGt | Pop the top of the stack and use its value as a key. Reposition cursor P1 so that it points to the smallest entry that is greater than the key from the stack. If there are no records greater than the key and P2 is not zero, then jump to P2. See also: Found, NotFound, Distinct, MoveLt, MoveGe, MoveLe
MoveLe | Pop the top of the stack and use its value as a key. Reposition cursor P1 so that it points to the largest entry that is less than or equal to the key that was popped from the stack. If there are no records less than or eqal to the key and P2 is not zero, then jump to P2. See also: Found, NotFound, Distinct, MoveGt, MoveGe, MoveLt
MoveLt | Pop the top of the stack and use its value as a key. Reposition cursor P1 so that it points to the largest entry that is less than the key from the stack. If there are no records less than the key and P2 is not zero, then jump to P2. See also: Found, NotFound, Distinct, MoveGt, MoveGe, MoveLe
Multiply | Pop the top two elements from the stack, multiply them together, and push the result back onto the stack. If either element is a string then it is converted to a double using the atof() function before the multiplication. If either operand is NULL, the result is NULL.
MustBeInt | Force the top of the stack to be an integer. If the top of the stack is not an integer and cannot be converted into an integer with out data loss, then jump immediately to P2, or if P2==0 raise an SQLITE_MISMATCH exception. If the top of the stack is not an integer and P2 is not zero and P1 is 1, then the stack is popped. In all other cases, the depth of the stack is unchanged.
Ne | This works just like the Eq opcode except that the jump is taken if the operands from the stack are not equal. See the Eq opcode for additional information.
Negative | Treat the top of the stack as a numeric quantity. Replace it with its additive inverse. If the top of the stack is NULL its value is unchanged.
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 pushed onto the stack. If P2>0 then P2 is a memory cell 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, a SQLITE_FULL error is generated. The P2 memory cell is updated with the generated record number. This P2 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. See also: Prev
Noop | Do nothing. This instruction is often useful as a jump destination.
Not | Interpret the top of the stack as a boolean value. Replace it with its complement. If the top of the stack is NULL its value is unchanged.
NotExists | Use the top of the stack as a integer key. If a record with that key does not exist in table of P1, then jump to P2. If the record does exist, then fall thru. The cursor is left pointing to the record if it exists. The integer key is popped from the stack. The difference between this operation and NotFound is that this operation assumes the key is an integer and that P1 is a table whereas NotFound assumes key is a blob constructed from MakeRecord and P1 is an index. See also: Distinct, Found, MoveTo, NotFound, IsUnique
NotFound | The top of the stack holds a blob constructed by MakeRecord. P1 is an index. If no entry exists in P1 that matches the blob then jump to P2. If an entry does existing, fall through. The cursor is left pointing to the entry that matches. The blob is popped from the stack. The difference between this operation and Distinct is that Distinct does not pop the key from the stack. See also: Distinct, Found, MoveTo, NotExists, IsUnique
NotNull | Jump to P2 if the top abs(P1) values on the stack are all not NULL. Regardless of whether or not the jump is taken, pop the stack P1 times if P1 is greater than zero. But if P1 is negative, leave the stack unchanged.
Null | Push a NULL onto the stack.
NullRow | Move the cursor P1 to a null row. Any OP_Column operations that occur while the cursor is on the null row will always push a NULL onto the stack.
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 transient or virtual table is deleted automatically when the cursor is closed. P2 is the number of columns in the virtual table. The cursor points to a BTree table if P3==0 and to a BTree index if P3 is not 0. If P3 is not NULL, it points to a KeyInfo structure that defines the format of keys in the index. This opcode was once called OpenTemp. But that created confusion because the term "temp table", might refer either to a TEMP table at the SQL level, or to a table opened by this opcode. Then this opcode was call OpenVirtual. But that created confusion with the whole virtual-table idea.
OpenPseudo | Open a new cursor that points to a fake table that contains a single row of data. Any attempt to write a second row of data causes the first row to be deleted. All data is deleted when the cursor is closed. A pseudo-table created by this opcode is useful for holding the NEW or OLD tables in a trigger. Also used to hold the a single row output from the sorter so that the row can be decomposed into individual columns using the OP_Column opcode.
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 an integer from the top of the stack. 0 means the main database and 1 means the database used for temporary tables. 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 P2==0 then take the root page number from the next of the stack. 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 P3 value is a pointer to a KeyInfo structure that defines the content and collating sequence of indices. P3 is NULL for cursors that are not pointing to indices. See also OpenWrite.
OpenWrite | Open a read/write cursor named P1 on the table or index whose root page is P2. If P2==0 then take the root page number from the stack. The P3 value is a pointer to a KeyInfo structure that defines the content and collating sequence of indices. P3 is NULL for cursors that are not pointing to indices. 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 | Pop two values off the stack. Take the logical OR of the two values and push the resulting boolean value back onto the stack.
ParseSchema | Read and parse all entries from the SQLITE_MASTER table of database P1 that match the WHERE clause P3. P2 is the "force" flag. Always do the parsing if P2 is true. If P2 is false, then this routine is a no-op if the schema is not currently loaded. In other words, if P2 is false, the SQLITE_MASTER table is only parsed if the rest of the schema is already loaded into the symbol table. This opcode invokes the parser to create a new virtual machine, then runs the new virtual machine. It is thus a reentrant opcode.
Pop | P1 elements are popped off of the top of stack and discarded.
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.
Pull | The P1-th element is removed from its current location on the stack and pushed back on top of the stack. The top of the stack is element 0, so "Pull 0 0 0" is a no-op. "Pull 1 0 0" swaps the top two elements of the stack. See also the Dup instruction.
Push | Overwrite the value of the P1-th element down on the stack (P1==0 is the top of the stack) with the value of the top of the stack. Then pop the top of the stack.
ReadCookie | Read cookie number P2 from database P1 and push it onto the stack. P2==0 is the schema version. P2==1 is the database format. P2==2 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. If P1 is negative, then this is a request to read the size of a databases free-list. P2 must be set to 1 in this case. The actual database accessed is ((P1+1)*-1). For example, a P1 parameter of -1 corresponds to database 0 ("main"), a P1 of -2 is database 1 ("temp"). 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 | P3 is a pointer to a 64-bit floating point value. Push that value onto the stack.
RealAffinity | If the top of the stack is 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 | Pop the top two elements from the stack, divide the first (what was on top of the stack) from the second (the next on stack) and push the remainder after division onto the stack. If either element is a string then it is converted to a double using the atof() function before the division. Division by zero returns NULL. If either operand is NULL, the result is NULL.
ResetCount | This opcode resets the VMs internal change counter to 0. If P1 is true, then the value of the change counter is copied to the database handle change counter (returned by subsequent calls to sqlite3_changes()) before it is reset. This is used by trigger programs.
Return | Jump immediately to the next instruction after the last unreturned OP_Gosub. If an OP_Return has occurred for all OP_Gosubs, then processing aborts with a fatal error.
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.
RowData | Push onto the stack the complete row data for cursor P1. There is no interpretation of the data. It is just copied onto the stack exactly as it is found in the database file. If the cursor is not pointing to a valid row, a NULL is pushed onto the stack.
Rowid | Push onto the stack an integer which is the key of the table entry that P1 is currently point to.
RowKey | Push onto the stack the complete row key for cursor P1. There is no interpretation of the key. It is just copied onto the stack exactly as it is found in the database file. If the cursor is not pointing to a valid row, a NULL is pushed onto the stack.
Sequence | Push an integer onto the stack which is the next available sequence number for cursor P1. The sequence number on the cursor is incremented after the push.
SetCookie | Write the top of the stack into cookie number P2 of database P1. P2==0 is the schema version. P2==1 is the database format. P2==2 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.
SetNumColumns | Before the OP_Column opcode can be executed on a cursor, this opcode must be called to set the number of fields in the table. This opcode sets the number of columns for cursor P1 to P2. If OP_KeyAsData is to be applied to cursor P1, it must be executed before this op-code.
ShiftLeft | Pop the top two elements from the stack. Convert both elements to integers. Push back onto the stack the second element shifted left by N bits where N is the top element on the stack. If either operand is NULL, the result is NULL.
ShiftRight | Pop the top two elements from the stack. Convert both elements to integers. Push back onto the stack the second element shifted right by N bits where N is the top element on the stack. If either operand is NULL, the result is NULL.
Sort | This opcode does exactly the same thing as OP_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 OP_Sort opcode instead of OP_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.
Statement | Begin an individual statement transaction which is part of a larger BEGIN..COMMIT transaction. This is needed so that the statement can be rolled back after an error without having to roll back the entire transaction. The statement transaction will automatically commit when the VDBE halts. The statement is begun on the database file with index P1. The main database file has an index of 0 and the file used for temporary tables has an index of 1.
String | The string value P3 of length P1 (bytes) is pushed onto the stack.
String8 | P3 points to a nul terminated UTF-8 string. This opcode is transformed into an OP_String before it is executed for the first time.
Subtract | Pop the top two elements from the stack, subtract the first (what was on top of the stack) from the second (the next on stack) and push the result back onto the stack. If either element is a string then it is converted to a double using the atof() function before the subtraction. If either operand 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. If P1 is not negative, then it is the index of the database in sqlite3.aDb[] and a read-lock is required. If P1 is negative, a write-lock is required. In this case the index of the database is the absolute value of P1 minus one (iDb = abs(P1) - 1;) and a write-lock is required. P2 contains the root-page of the table to lock. P3 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.
ToBlob | Force the value on the top of the stack to be a BLOB. If the value is numeric, convert it to a string first. Strings are simply reinterpreted as blobs with no change to the underlying data. A NULL value is not changed by this routine. It remains NULL.
ToInt | Force the value on the top of the stack to be an integer. If The value is currently a real number, drop its fractional part. If the value is text or blob, try to convert it to an integer using the equivalent of atoi() and store 0 if no such conversion is possible. A NULL value is not changed by this routine. It remains NULL.
ToNumeric | Force the value on the top of the stack to be numeric (either an integer or a floating-point number.) If the value is text or blob, try to convert it to an using the equivalent of atoi() or atof() and store 0 if no such conversion is possible. A NULL value is not changed by this routine. It remains NULL.
ToReal | Force the value on the top of the stack to be a floating point number. If The value is currently an integer, convert it. If the value is text or blob, try to convert it to an integer using the equivalent of atoi() and store 0 if no such conversion is possible. A NULL value is not changed by this routine. It remains NULL.
ToText | Force the value on the top of the stack to be text. If the value is numeric, convert it to a string using the equivalent of printf(). Blob values are unchanged and are afterwards simply interpreted as text. A NULL value is not changed by this routine. It remains NULL.
Transaction | Begin a transaction. The transaction ends when a Commit or Rollback opcode is encountered. Depending on the ON CONFLICT setting, the transaction might also be rolled back if an error is encountered. 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. If P2 is non-zero, then a write-transaction is started. A RESERVED lock is obtained on the database file when a write-transaction is started. No other process can start another write transaction while this transaction is underway. Starting a write transaction also creates a rollback journal. A write transaction must be started before any changes can be made to the database. If P2 is 2 or greater then an EXCLUSIVE lock is also obtained on the file. If P2 is zero, then a read-lock is obtained on the database file.
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 | Push the value of variable P1 onto the stack. A variable is an unknown in the original SQL string as handed to sqlite3_compile(). Any occurance of the '?' character in the original SQL is considered a variable. Variables in the SQL string are number from left to right beginning with 1. The values of variables are set using the sqlite3_bind() API.
VBegin | P3 a pointer to an sqlite3_vtab structure. Call the xBegin method for that table.
VColumn | Push onto the stack the value of the P2-th column of the row of the virtual-table that the P1 cursor is pointing to.
VCreate | P3 is the name of a virtual table in database P1. Call the xCreate method for that table.
VDestroy | P3 is the name of a virtual table in database P1. Call the xDestroy method of that table.
VerifyCookie | Check the value of global database parameter number 0 (the schema version) and make sure it is equal to P2. P1 is the database number which is 0 for the main database file and 1 for the file holding temporary tables and some higher number for auxiliary databases. 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. Either a transaction needs to have been started or an OP_Open needs to be executed (to establish a read lock) before this opcode is invoked.
VFilter | P1 is a cursor opened using VOpen. P2 is an address to jump to if the filtered result set is empty. P3 is either NULL or a string that was generated by the xBestIndex method of the module. The interpretation of the P3 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 the top of the stack. Next down on the stack is the argc parameter. Beneath the next of stack are argc additional parameters which are passed to xFilter as argv. The topmost parameter (i.e. 3rd element popped from the stack) becomes argv[argc-1] when passed to xFilter. The integer query plan parameter, argc, and all argv stack values are popped from the stack before this instruction completes. 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 | P3 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 | P3 is a pointer to a virtual table object, an sqlite3_vtab structure. This opcode invokes the corresponding xRename method. The value on the top of the stack is popped and passed as the zName argument to the xRename method.
VRowid | Push an integer onto the stack which is the rowid of the virtual-table that the P1 cursor is pointing to.
VUpdate | P3 is a pointer to a virtual table object, an sqlite3_vtab structure. This opcode invokes the corresponding xUpdate method. P2 values are taken from the stack to pass to the xUpdate invocation. The value on the top of the stack 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 the P2-th element down on the stack) 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 higher elements in the stack 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.

This page last modified 2007/11/12 15:21:49 UTC