MySql只支援Union(並集)集合運算，好像也是4.0以後才有的；但是對於交集Intersect、差集Except，就沒有實現了。

一般的解決方案用in和not in來解決，小量資料還可以，但資料量大了效率就很低了
建立table1

/*DDL 資訊*/------------

CREATE TABLE `t1` (
  `id` int(11) NOT NULL,
  `name` varchar(20) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
 

/*DDL 資訊*/------------

CREATE TABLE `t2` (
  `id` int(11) NOT NULL,
  `name` varchar(20) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

INSERT INTO t1 VALUES(1,'小王',10);
INSERT INTO t1 VALUES(2,'小宋',20);
INSERT INTO t1 VALUES(3,'小白',30);
INSERT INTO t1 VALUES(4,'hello',40);


INSERT INTO t2 VALUES(1,'小王',10);
INSERT INTO t2 VALUES(2,'小宋',22);
INSERT INTO t2 VALUES(3,'小肖',31);
INSERT INTO t2 VALUES(4,'hello',40);
 

	SELECT t1.* FROM t1 
	
	id	name	age
	1	小王	    10
	2	小宋	    20
	3	小白	    30
	4	hello	40

	SELECT t2.* FROM t2 
	
	id	name	age
	1	小王	10
	2	小宋	22
	3	小肖	31
	4	hello	40

使用not in 求差集，但效率低

	SELECT t1.* FROM t1 
	WHERE 
	name NOT IN
	(SELECT name FROM t2)
	
	id	name	age
	3	小白	    30

    SELECT t1.id, t1.name, t1.age
    FROM t1 
    LEFT JOIN t2 
    ON t1.id = t2.id
    WHERE t1.name != t2.name
    
       OR t1.age != t2.age;
    
    
    id	name	age
    2	小宋	    20
    3	小白	    30
 

SELECT  id,  NAME,  age, COUNT(*)
    FROM (SELECT id, NAME, age
        FROM t1
        
        UNION ALL
        
        SELECT id, NAME, age
        FROM t2
        ) a
    GROUP BY id, NAME, age
    HAVING COUNT(*) > 1
    
    id	NAME	age	COUNT(*)
    1	小王	    10	2
    4	hello	40	2