如何比较mysql存储过程中的两列值

Question

我想使用连接来获取两列，下面的查询工作正常，现在我怎么可以比较这两个值使用if语句。

SELECT 
    failed = L.failed_attempts AS 'FAILED ATTEMPTS', 
    s_value = s.setting_value as 'SETTING VALUE' 
FROM login_t L 
INNER JOIN settings_t S ON S.SETTING_NAME = 'login_attempts' 
WHERE L.login_id = id 
    AND L.failed_attempts > S.setting_value; 

如果failed_attempts > settings_value然后在login_t的is_logged_in列的值更新为0，返回false，否则返回true

PS：我使用MySQL的存储过程

Answer 1

如果你的select语句百达retuns恰好一行，您可以存储选定的值INTO局部变量，您应该首先使用DECALRE。然后您可以使用IF .. THEN .. ELSE .. END IF;：返回您只需要的东西SELECT someValue。 我不知道应该比较什么。但是，这是这样的，你可以做到这一点：

DECLARE FAILED_ATTEMPTS INT; 
DECLARE SETTING_VALUE INT; 

SELECT 
    failed = L.failed_attempts, 
    s_value = s.setting_value 
INTO 
    FAILED_ATTEMPTS, 
    SETTING_VALUE 
FROM login_t L 
INNER JOIN settings_t S ON S.SETTING_NAME = 'login_attempts' 
WHERE L.login_id = id 
    AND L.failed_attempts > S.setting_value; 

IF FAILED_ATTEMPTS > SETTING_VALUE 
THEN 
    -- your update statement here 
    SELECT FALSE; 
ELSE 
    SELECT TRUE; 
END IF; 

也许你需要

SELECT 
    L.failed_attempts, 
    s.setting_value 
INTO 
    FAILED_ATTEMPTS, 
    SETTING_VALUE 

但不知何故，我猜你需要两个SELECT语句：

SELECT L.failed_attempts, 
INTO FAILED_ATTEMPTS 
FROM login_t L 
WHERE L.login_id = id; 

SELECT s.setting_value 
INTO SETTING_VALUE 
FROM settings_t S 
WHERE S.SETTING_NAME = 'login_attempts';