如何从MySQL中退出外部if语句

你可以试试相反的情况:

IF (true) THEN
    /* do some work here */
    IF (NOT somethingWrong) THEN
        /* Do whatever is remaining to do in this outer IF block */
    END IF;
END IF;

如果你有多个这样的例子,那么你可能不想嵌套 IF 这样的积木:

IF (true) THEN
    /* do some work here */
    IF (NOT somethingWrong) THEN
        /* do some more work here */
        IF (NOT somethingWrong) THEN
            /* Do whatever is remaining to do in this outer IF block */
        END;
    END IF;
END IF;

…这可能会被深深地嵌套。而是使用一个变量(检查 SET 语法)可以跟踪错误情况并将 如果 就像这样:

SET err = 0
IF (true) THEN
    /* do some work here */
    IF (NOT err)
        /* do some more work here that maybe sets the err variable to some non-zero value */
    END IF;
    IF (NOT err)
        /* do some more work here that maybe sets the err variable non-zero */
    END IF;
    IF (NOT err)
        /* do the remaining work */
    END IF;
END IF;

你甚至可以用同样的原理在这里建立一些循环:

IF (true) THEN
    /* do some work here */
    IF (NOT err)
        /* do some more work here that maybe sets the err variable to some non-zero value */
    END IF;
    IF (NOT err)
        /* do some more work here that maybe sets the err variable non-zero */
    END IF;
    WHILE (NOT err AND some_loop_condition) DO
        /* some work that needs to repeat a few times, 
           but should be interrupted when err is non-zero */
    END WHILE
    IF (NOT err)
        /* do the remaining work */
    END IF;
END IF;

你可以用 loop construct 以下内容:

fauxloop: LOOP
    IF somethingIsWrong THEN
        LEAVE fauxloop;
    END IF;

    -- do some work here

    IF somethingElseIsWrong THEN
        LEAVE fauxloop;
    END IF;

    -- do some work here

    LEAVE fauxloop;
END LOOP fauxloop;