SPI_EXECUTE(3) PostgreSQL 9.2.7 Documentation SPI_EXECUTE(3)
SPI_execute - execute a command
int SPI_execute(const char * command, bool read_only, long count)
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 procedure.
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
It is generally unwise to mix read-only and read-write commands within a single function
using SPI; that could result in very confusing behavior, since the read-only queries would
not see the results of any database updates done by the read-write queries.
The actual number of rows for which the (last) command was executed is returned in the
global variable SPI_processed. If the return value of the function is SPI_OK_SELECT,
SPI_OK_INSERT_RETURNING, 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.
The structure SPITupleTable is defined thus:
MemoryContext tuptabcxt; /* memory context of result table */
uint32 alloced; /* number of alloced vals */
uint32 free; /* number of free vals */
TupleDesc tupdesc; /* row descriptor */
HeapTuple *vals; /* rows */
vals is an array of pointers to rows. (The number of valid entries is given by
SPI_processed.) tupdesc is a row descriptor which you can pass to SPI functions dealing
with rows. tuptabcxt, alloced, and free are internal fields not intended for use by SPI
SPI_finish frees all SPITupleTables allocated during the current procedure. You can free a
particular result table earlier, if you are done with it, by calling SPI_freetuptable.
const char * command
string containing command to execute
true for read-only execution
maximum number of rows to return, or 0 for no limit
If the execution of the command was successful then one of the following (nonnegative)
values will be returned:
if a SELECT (but not SELECT INTO) was executed
if a SELECT INTO was executed
if an INSERT was executed
if a DELETE was executed
if an UPDATE was executed
if an INSERT RETURNING was executed
if a DELETE RETURNING was executed
if an UPDATE RETURNING was executed
if a utility command (e.g., CREATE TABLE) was executed
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:
if command is NULL or count is less than 0
if COPY TO stdout or COPY FROM stdin was attempted
if a transaction manipulation command was attempted (BEGIN, COMMIT, ROLLBACK,
SAVEPOINT, PREPARE TRANSACTION, COMMIT PREPARED, ROLLBACK PREPARED, or any variant
if the command type is unknown (shouldn't happen)
if called from an unconnected procedure
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
procedure variables if you need to access the result table of SPI_execute or another
query-execution function across later calls.
PostgreSQL 9.2.7 2014-02-17 SPI_EXECUTE(3)