postgresql - 取消用户定义函数中的先前操作

Question

是否可以在用户定义的函数中取消之前的操作？

例如:

CREATE OR REPLACE FUNCTION transact_test () RETURNS BOOLEAN
AS $$
    BEGIN

        UPDATE table1 SET ...

        UPDATE table2 SET ...

        IF some_condition THEN
            --Here is  possible to cancel  all above operations?
            RETURN FALSE; 
        END IF;

        RETURN TRUE;
    END;
$$
LANGUAGE plpgsql;

Answer 1

到目前为止，这两个答案都不正确。
如果您尝试在 plpgsql 函数中启动事务或使用 SAVEPOINT，您会收到如下错误消息:

ERROR:  cannot begin/end transactions in PL/pgSQL
HINT:  Use a BEGIN block with an EXCEPTION clause instead.
CONTEXT:  PL/pgSQL function "f_savepoint" line 6 at SQL statement

如果您在普通 SQL 函数中尝试 SAVEPOINT:

ERROR:  SAVEPOINT is not allowed in a SQL function
CONTEXT:  SQL function "f_savepoint2" during startup

按照错误消息的指示，使用 BEGIN block而不是在 plpgsql 函数中。您的演示可能如下所示:

CREATE OR REPLACE FUNCTION transact_test(boolean)
  RETURNS boolean AS
$func$
BEGIN -- start a nested BEGIN block
    UPDATE t SET i = i+1 WHERE i = 1;
    UPDATE t SET i = i+1 WHERE i = 3;
    IF $1 THEN
        RAISE EXCEPTION 'foo';  -- cancels all of the above
    END IF;

    RETURN TRUE;

EXCEPTION WHEN OTHERS THEN
    RETURN FALSE; 
    -- do nothing
END
$func$ LANGUAGE plpgsql;

-> SQLfiddle展示这一切。