SPI_EXECUTE(3) PostgreSQL 9.3.2 Documentation SPI_EXECUTE(3)NAMESPI_execute - execute a command
SYNOPSIS
int SPI_execute(const char * command, bool read_only, long count)
DESCRIPTIONSPI_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 results.
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. 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
{
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 */
} SPITupleTable;
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 callers.
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.
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_UPDATE
if an UPDATE 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 procedure
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 procedure variables if you
need to access the result table of SPI_execute or another
query-execution function across later calls.
PostgreSQL 9.3.2 2013 SPI_EXECUTE(3)
