MySQL的IF ... THEN接着是查询语句

Question

是这样的有效MySQL中：

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

用途：

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 

一直尽量减少遍数在一个表来获得你想要的结果。 SQL是基于SET的，而不是过程性的 - 当它接近正确时，SQL对你更好。