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SPI_EXECUTE(3) PostgreSQL 15.4 Documentation SPI_EXECUTE(3)
NAME SPI_execute - execute a command
SYNOPSIS int SPI_execute(const char * command, bool read_only, long count)
DESCRIPTION SPI_execute executes the specified SQL command for count rows. If read_only is true, the command must be read-only, and execution overhead is somewhat reduced.
This function can only be called from a connected C function.
If count is zero then the command is executed for all rows that it applies to. If count is greater than zero, then no more than count rows will be retrieved; execution stops when the count is reached, much like adding a LIMIT clause to the query. For example,
SPI_execute("SELECT * FROM foo", true, 5);
will retrieve at most 5 rows from the table. Note that such a limit is only effective when the command actually returns rows. For example,
SPI_execute("INSERT INTO foo SELECT * FROM bar", false, 5);
inserts all rows from bar, ignoring the count parameter. However, with
SPI_execute("INSERT INTO foo SELECT * FROM bar RETURNING *", false, 5);
at most 5 rows would be inserted, since execution would stop after the fifth RETURNING result row is retrieved.
You can pass multiple commands in one string; SPI_execute returns the result for the command executed last. The count limit applies to each command separately (even though only the last result will actually be returned). The limit is not applied to any hidden commands generated by rules.
When read_only is false, SPI_execute increments the command counter and computes a new snapshot before executing each command in the string. The snapshot does not actually change if the current transaction isolation level is SERIALIZABLE or REPEATABLE READ, but in READ COMMITTED mode the snapshot update allows each command to see the results of newly committed transactions from other sessions. This is essential for consistent behavior when the commands are modifying the database.
When read_only is true, SPI_execute does not update either the snapshot or the command counter, and it allows only plain SELECT commands to appear in the command string. The commands are executed using the snapshot previously established for the surrounding query. This execution mode is somewhat faster than the read/write mode due to eliminating per-command overhead. It also allows genuinely stable functions to be built: since successive executions will all use the same snapshot, there will be no change in the results.
It is generally unwise to mix read-only and read-write commands within SPI_OK_DELETE_RETURNING, or SPI_OK_UPDATE_RETURNING, then you can use the global pointer SPITupleTable *SPI_tuptable to access the result rows. Some utility commands (such as EXPLAIN) also return row sets, and SPI_tuptable will contain the result in these cases too. Some utility commands (COPY, CREATE TABLE AS) don't return a row set, so SPI_tuptable is NULL, but they still return the number of rows processed in SPI_processed.
The structure SPITupleTable is defined thus:
typedef struct SPITupleTable { /* Public members */ TupleDesc tupdesc; /* tuple descriptor */ HeapTuple *vals; /* array of tuples */ uint64 numvals; /* number of valid tuples */
/* Private members, not intended for external callers */ uint64 alloced; /* allocated length of vals array */ MemoryContext tuptabcxt; /* memory context of result table */ slist_node next; /* link for internal bookkeeping */ SubTransactionId subid; /* subxact in which tuptable was created */ } SPITupleTable;
The fields tupdesc, vals, and numvals can be used by SPI callers; the remaining fields are internal. vals is an array of pointers to rows. The number of rows is given by numvals (for somewhat historical reasons, this count is also returned in SPI_processed). tupdesc is a row descriptor which you can pass to SPI functions dealing with rows.
SPI_finish frees all SPITupleTables allocated during the current C function. You can free a particular result table earlier, if you are done with it, by calling SPI_freetuptable.
ARGUMENTS const char * command string containing command to execute
bool read_only true for read-only execution
long count maximum number of rows to return, or 0 for no limit
RETURN VALUE If the execution of the command was successful then one of the following (nonnegative) values will be returned:
SPI_OK_SELECT if a SELECT (but not SELECT INTO) was executed
SPI_OK_SELINTO if a SELECT INTO was executed
SPI_OK_INSERT if an INSERT was executed
SPI_OK_DELETE if a DELETE was executed
SPI_OK_INSERT_RETURNING if an INSERT RETURNING was executed
SPI_OK_DELETE_RETURNING if a DELETE RETURNING was executed
SPI_OK_UPDATE_RETURNING if an UPDATE RETURNING was executed
SPI_OK_UTILITY if a utility command (e.g., CREATE TABLE) was executed
SPI_OK_REWRITTEN if the command was rewritten into another kind of command (e.g., UPDATE became an INSERT) by a rule.
On error, one of the following negative values is returned:
SPI_ERROR_ARGUMENT if command is NULL or count is less than 0
SPI_ERROR_COPY if COPY TO stdout or COPY FROM stdin was attempted
SPI_ERROR_TRANSACTION if a transaction manipulation command was attempted (BEGIN, COMMIT, ROLLBACK, SAVEPOINT, PREPARE TRANSACTION, COMMIT PREPARED, ROLLBACK PREPARED, or any variant thereof)
SPI_ERROR_OPUNKNOWN if the command type is unknown (shouldn't happen)
SPI_ERROR_UNCONNECTED if called from an unconnected C function
NOTES All SPI query-execution functions set both SPI_processed and SPI_tuptable (just the pointer, not the contents of the structure). Save these two global variables into local C function variables if you need to access the result table of SPI_execute or another query-execution function across later calls.
PostgreSQL 15.4 2023 SPI_EXECUTE(3)