39.5. ����

����һ���dz��򵥵� SPI ʹ�õ����ӡ� ���� execq �����һ�����������һ�� SQL ��� �ڶ�����������һ���м����� �� SPI_exec ִ�������ѯ���ҷ��ز�ѯִ�й��ļ�¼������ ������� src/test/regress/regress.c �� contrib/spi ���Ҹ����ӵ����ӡ�

#include "executor/spi.h"   /* ʹ�� SPI ʱ��Ҫ��ͷ�ļ� */

int execq(text *sql, int cnt);

int
execq(text *sql, int cnt)
{
    char *command;
    int ret;
    int proc;

    /* �Ѹ����� text ����ת���� C �ִ� */
    query = DatumGetCString(DirectFunctionCall1(textout,
                                                PointerGetDatum(sql)));

    SPI_connect();
    
    ret = SPI_exec(command, cnt);
    
    proc = SPI_processed;
    /*
     * ������� SELECT ����ȡ����һЩԪ�� - 
     * ͨ�� elog (INFO) ������� RETURNS Ԫ��
     */
    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++)
                spnrintf(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);
}

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CREATE FUNCTION execq(text, integer) RETURNS integer
    AS 'filename'
    LANGUAGE C;

������һ���Ự���ӣ�

=> 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    -- execq ���� 0 ��
INFO:  EXECQ:  1    -- execq ���أ����ϲ� 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��ֻ������һ�� �� ��������������

 execq
-------
     3              -- 10 ֻ�����ֵ��3 ����ʵ������
(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                  -- �� (0) + 1 ����û����
(1 row)

=> INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1);
INFO:  EXECQ:  0
INSERT 167713 1
=> SELECT * FROM a;
 x
---
 1
 2                  -- �� a + 1 ������һ��
(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 �� * 1 ��x �� ��һ�У�
 6                  -- 3 ��   (2 + 1 �ող����) * 2 (�ڶ������ x)
(4 rows)               ^^^^^^
                       �ڲ�ͬ�ĵ����� execq() �����Ķ�����ͬ