Question

我正在尝试使用连接获取两列，以下查询工作正常，现在我如何使用if语句比较这两个值。

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，则将is_logged_in中的login_t列值更新为0并返回false，否则返回true

PS：我正在使用mysql存储过程

Answer 1

如果你的select语句总是只返回一行，你可以存储选定的值INTO局部变量，你应该先DECALRE。然后，您可以使用IF .. THEN .. ELSE .. END IF;：返回您需要的内容SELECT someValue。我不是应该比得上的。但这就是方法，你可以这样做：

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

但不知怎的，我想你需要两个选择语句：

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';

如何比较mysql存储过程中的两个列值

1 个答案: