mysql - MySQL IF...THEN 后跟查询语句

Question

这样的东西在 MySQL 中是否有效：

DELIMITER //
CREATE FUNCTION LOGIN_VALIDATE(IN uName VARCHAR(32),IN uPass VARCHAR(32))
RETURNS BOOLEAN
BEGIN
    DECLARE row_count BOOLEAN DEFAULT 0;
    DECLARE stored_pass VARCHAR(32) DEFAULT NULL;
    DECLARE valid_return BOOLEAN DEFAULT 0;
    SELECT count(*) INTO row_count FROM Login WHERE userId='uName';
    IF row_count = 1 THEN 
        SELECT pWord INTO stored_pass FROM Login WHERE userId='uName';
    END IF;
    IF stored_pass = 'uPass' THEN 
        SET valid_return = 1;
    END IF;
    RETURN valid_return;
END //
DELIMITER ;

Answer 1

采用：

DECLARE valid_return BOOLEAN DEFAULT 0;

SELECT CASE WHEN COUNT(*) = 1 THEN 1 ELSE 0 END
  INTO valid_return
  FROM LOGIN l
 WHERE l.userid = @uName
   AND l.pword = @uPass

始终尽量减少通过桌子的次数以获得所需的结果。SQL 是基于 SET 的，而不是过程式的——当正确使用 SQL 时，它会更好地为您工作。