如何从MYSQL中的外部IF语句退出答案

【问题标题】：How to exit from outer IF statement in MYSQL如何从MYSQL中的外部IF语句退出
【发布时间】：2018-07-12 11:13:45
【问题描述】：

如何退出外层IF语句，继续存储过程

IF (true) THEN

    -- do some work here

    IF (somethingWrong=true) THEN
        -- Exit from the outer IF and continue SP
    END IF;

    -- do some work here
END IF;

【问题讨论】：

您现在拥有代码的方式，无论内部条件是否为真，执行都会以任何方式退出外部IF 块。您到底在寻找什么？
IF (somethingWrong==true) THEN == 在 MySQL 中不存在 (sqlfiddle.com/#!9/340e01/441) 你需要使用 = 来检查等于

标签： mysql if-statement stored-procedures

【解决方案1】：

你可以只测试相反的条件：

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;

如果您有多个实例想要像这样退出，那么您可能不想像这样嵌套 IF 块：

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;

...这可以深入嵌套。而是使用一个变量（检查SET 语法）来跟踪错误情况并扁平化您的IFs。像这样的：

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;

您甚至可以在其中有一些具有相同原理的循环：

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;

【讨论】：