mysql 中 and 与&& 区别与用法

CREATE FUNCTION `get_times_weeek` (   last_accting_date DATETIME,   nursePerformTime VARCHAR (50) ) RETURNS INT (11) COMMENT '计算以周为单位的计费次数'  BEGIN   DECLARE return_val INT DEFAULT 0 ;   DECLARE flag BOOLEAN DEFAULT FALSE ;   DECLARE weekNo INT ;   DECLARE s_index INT ;   IF last_accting_date IS NOT NULL && DATE_FORMAT(NOW(), '%Y-%m-%d') = DATE_FORMAT(last_accting_date, '%Y-%m-%d')    THEN SET return_val = 0 ;   ELSE    SELECT      DAYOFWEEK(NOW()) INTO weekNo ;   IF weekNo = 1    THEN SET weekNo = 7 ;   ELSE SET weekNo = weekNo - 1 ;   END IF ;   SELECT      LOCATE(weekNo, nursePerformTime) INTO s_index ;   IF s_index > 0    THEN SET return_val = 1 ;   ELSE SET return_val = 0 ;   END IF ;   END IF ;   RETURN return_val ;

END 

总结： and 用于where 条件中拼接条件 && 用于 if 逻辑判断。