有兩個表：SPEC1、tmpDOT
SPEC1種一列為：HIGH
tmpDOT共有兩個：OLD、NEW
兩個表的內容大概如下：
SPEC1:
... HIGH ...
... A    ...
... B    ...
... A    ...
... C    ...
... B    ...
... D    ...

tmpDOT：
OLD   NEW
A     newA
B     newB

C     newC

方法一

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1. update a set HIGH=b.NEW  from SPEC1 a,tmpDOT  b   
2. where a.high=b.old  

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1. UPDATE A  
2. SET HIGH=B.NEW  
3. FROM A LEFT JOIN B ON (A.HIGH=B.OLD)  

一個復雜的栗子：一個更新多個字段的例子

UPDATE A JOIN B ON A.XX= B.XX

SET A.Y = B.Y,   A.Z=B.Z

-- 正式版本 最終版 統計上班排名和時間
	UPDATE mobile_user_total AS old 
	INNER JOIN 
		(
			SELECT u_info.user_id, class.class_name, u_info.`name`, a.clock_date AS arrive_time, COUNT(b.user_id)+1 AS up_rank
			FROM user_info u_info 
			JOIN user_class u_class ON u_info.user_id = u_class.user_id
			JOIN class ON class.id = u_class.class_id
			JOIN 
					# a 表作為考勤主表用來統計用戶沒有遲到的最早記錄
					(
					SELECT u_clock.user_id, MIN(clock_date) AS clock_date, u_class.class_id
					FROM user_clockrecords u_clock
					JOIN user_class u_class ON u_class.user_id = u_clock.user_id
					JOIN class ON u_class.class_id = class.id
					WHERE DATE(clock_date) = cal_date AND DATE_FORMAT(u_clock.clock_date,'%H:%i:%s') < DATE_FORMAT(class.begin_time,'%H:%i:%s')	#根據傳入的日期
					GROUP BY user_id
					)AS a ON u_info.user_id = a.user_id	
					LEFT JOIN(
					SELECT u_clock.user_id, MIN(clock_date) AS clock_date, u_class.class_id
					FROM user_clockrecords u_clock
					JOIN user_class u_class ON u_class.user_id = u_clock.user_id
					JOIN class ON u_class.class_id = class.id
					WHERE DATE(clock_date) = cal_date AND DATE_FORMAT(u_clock.clock_date,'%H:%i:%s') < DATE_FORMAT(class.begin_time,'%H:%i:%s')	#根據傳入的日期
				GROUP BY user_id
				)AS b ON a.class_id = b.class_id AND u_info.user_id <> b.user_id AND b.clock_date < a.clock_date
			GROUP BY u_info.user_id
		)AS new	ON old.user_id = new.user_id AND old.`current_time` = cal_date		#根據傳入的日期
	SET old.work_clock_time = new.arrive_time, old.up_ranking = new.up_rank;

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1. update  a  
2.   set high  = (select new from tmpdot where old=a.high  )  
3.    from spec1 a