PostgreSQL WHENEVER

描述

定義一個(gè)行為，它會(huì)在 SQL 執(zhí)行結(jié)果的特殊情況（行未找到、SQL 警告或錯(cuò)誤）中被調(diào)用。

參數(shù)

參數(shù)描述見第 35.8.1 節(jié)。

例子

EXEC SQL WHENEVER NOT FOUND CONTINUE;
EXEC SQL WHENEVER NOT FOUND DO BREAK;
EXEC SQL WHENEVER NOT FOUND DO CONTINUE;
EXEC SQL WHENEVER SQLWARNING SQLPRINT;
EXEC SQL WHENEVER SQLWARNING DO warn();
EXEC SQL WHENEVER SQLERROR sqlprint;
EXEC SQL WHENEVER SQLERROR CALL print2();
EXEC SQL WHENEVER SQLERROR DO handle_error("select");
EXEC SQL WHENEVER SQLERROR DO sqlnotice(NULL, NONO);
EXEC SQL WHENEVER SQLERROR DO sqlprint();
EXEC SQL WHENEVER SQLERROR GOTO error_label;
EXEC SQL WHENEVER SQLERROR STOP;

一個(gè)典型的應(yīng)用是使用WHENEVER NOT FOUND BREAK來處理通過結(jié)果集的循環(huán)：

int
main(void)
{
    EXEC SQL CONNECT TO testdb AS con1;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;
    EXEC SQL ALLOCATE DESCRIPTOR d;
    EXEC SQL DECLARE cur CURSOR FOR SELECT current_database(), 'hoge', 256;
    EXEC SQL OPEN cur;

    /* 當(dāng)?shù)竭_(dá)結(jié)果集末尾時(shí)，跳出循環(huán) */
    EXEC SQL WHENEVER NOT FOUND DO BREAK;

    while (1)
    {
        EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d;
        ...
    }

    EXEC SQL CLOSE cur;
    EXEC SQL COMMIT;

    EXEC SQL DEALLOCATE DESCRIPTOR d;
    EXEC SQL DISCONNECT ALL;

    return 0;
}

兼容性

SQL 標(biāo)準(zhǔn)中說明了WHENEVER，但是大部分動(dòng)作是 PostgreSQL 擴(kuò)展。