This section contains a very simple example of SPI usage. The procedure execq takes an SQL command as its first argument and a row count as its second, executes the command using SPI_exec and returns the number of rows that were processed by the command. You can find more complex examples for SPI in the source tree in src/test/regress/regress.c and in contrib/spi.
#include "executor/spi.h" int execq(text *sql, int cnt); int execq(text *sql, int cnt) { char *command; int ret; int proc; /* Convert given text object to a C string */ command = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(sql))); SPI_connect(); ret = SPI_exec(command, cnt); proc = SPI_processed; /* * If this is a SELECT and some rows were fetched, * then the rows are printed via elog(INFO). */ if (ret == SPI_OK_SELECT && SPI_processed > 0) { TupleDesc tupdesc = SPI_tuptable->tupdesc; SPITupleTable *tuptable = SPI_tuptable; char buf[8192]; int i, j; for (j = 0; j < proc; j++) { HeapTuple tuple = tuptable->vals[j]; for (i = 1, buf[0] = 0; i <= tupdesc->natts; i++) snprintf(buf + strlen (buf), sizeof(buf) - strlen(buf), " %s%s", SPI_getvalue(tuple, tupdesc, i), (i == tupdesc->natts) ? " " : " |"); elog (INFO, "EXECQ: %s", buf); } } SPI_finish(); pfree(command); return (proc); } (This function uses call convention version 0, to make the example easier to understand. In real applications you should user the new version 1 interface.)
This is how you declare the function after having compiled it into a shared library:
CREATE FUNCTION execq(text, integer) RETURNS integer AS 'filename' LANGUAGE C;
Here is a sample session:
=> SELECT execq('CREATE TABLE a (x integer)', 0); execq ------- 0 (1 row) => INSERT INTO a VALUES (execq('INSERT INTO a VALUES (0)', 0)); INSERT 167631 1 => SELECT execq('SELECT * FROM a', 0); INFO: EXECQ: 0 -- inserted by execq INFO: EXECQ: 1 -- returned by execq and inserted by upper INSERT execq ------- 2 (1 row) => SELECT execq('INSERT INTO a SELECT x + 2 FROM a', 1); execq ------- 1 (1 row) => SELECT execq('SELECT * FROM a', 10); INFO: EXECQ: 0 INFO: EXECQ: 1 INFO: EXECQ: 2 -- 0 + 2, only one row inserted - as specified execq ------- 3 -- 10 is the max value only, 3 is the real number of rows (1 row) => DELETE FROM a; DELETE 3 => INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1); INSERT 167712 1 => SELECT * FROM a; x --- 1 -- no rows in a (0) + 1 (1 row) => INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1); INFO: EXECQ: 0 INSERT 167713 1 => SELECT * FROM a; x --- 1 2 -- there was one row in a + 1 (2 rows) -- This demonstrates the data changes visibility rule: => INSERT INTO a SELECT execq('SELECT * FROM a', 0) * x FROM a; INFO: EXECQ: 1 INFO: EXECQ: 2 INFO: EXECQ: 1 INFO: EXECQ: 2 INFO: EXECQ: 2 INSERT 0 2 => SELECT * FROM a; x --- 1 2 2 -- 2 rows * 1 (x in first row) 6 -- 3 rows (2 + 1 just inserted) * 2 (x in second row) (4 rows) ^^^^^^ rows visible to execq() in different invocations
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