SQL Server中的集合运算: UNION, EXCEPT和INTERSECT示例代码详解

SQL Server中的集合运算包括UNION(合并),EXCEPT(差集)和INTERSECT(相交)三种。

集合运算的基本使用

1.UNION(合并两个查询结果集，隐式DINSTINCT，删除重复行)

--合并两个提取表/派生表(derived table), 返回结果为:[a,b,c,d,e]SELECT FC FROM (VALUES('a'),('b'),('c'),('e')) Table1 (FC)UNIONSELECT FC FROM (VALUES('a'),('b'),('c'),('d')) Table2 (FC)

--提取表/派生表(derived table)可以是多列，列名、顺序可以不同，但列数必须相同SELECT * FROM (VALUES('a','Anna'),('b','Bob'),('c','Cassie'),('e','Elina')) Table1 (FC, Name)UNION ALLSELECT * FROM (VALUES('a','Anna'),('b','Bob'),('c','Cassie'),('d','David')) Table2 (FC, Name)

--返回结果为:[e]SELECT FC FROM (VALUES('a'),('b'),('c'),('e')) Table1 (FC)EXCEPTSELECT FC FROM (VALUES('a'),('b'),('c'),('d')) Table2 (FC)

--返回结果为:[a,b,c]SELECT FC FROM (VALUES('a'),('b'),('c'),('e')) Table1 (FC)INTERSECTSELECT FC FROM (VALUES('a'),('b'),('c'),('d')) Table2 (FC)

1.使用UNION代替Where子句中的OR，查询速度更快

--使用Where子句 + ORSELECT name, population, area FROM world WHERE area > 3000000 OR population > 25000000--使用UNIONSELECT name, population, area FROM world WHERE area > 3000000UNIONSELECT name, population, area FROM world WHERE population > 25000000

假设存在表Customers, 数据如下表所示

cust_id	cust_name	cust_address	cust_city	cust_state	cust_country	cust_contact	cust_email
1000000001	Village Toys	200 Maple Lane	Detroit	MI	USA	John Smith	sales@villagetoys.com
1000000002	Kids Place	333 South Lake Drive	Columbus	OH	USA	Michelle Green	NULL
1000000003	Fun4All	1 Sunny Place	Muncie	IN	USA	Jim Jones	jjones@fun4all.com
1000000004	Fun4All	829 Riverside Drive	Phoenix	AZ	USA	Denise L. Stephens	dstephens@fun4all.com
1000000005	The Toy Store	4545 53rd Street	Chicago	IL	USA	Kim Howard	NULL

--过滤出列表中不存在于数据库中的项--返回结果为['1000000006','1000000007']SELECT [Id] AS [cust_id] FROM(VALUES('1000000004'),('1000000005'),('1000000006'),('1000000007')) dt ([Id])EXCEPTSELECT [cust_id] FROM [Customers]--过滤出列表中存在于数据库中的项--返回结果为['1000000004','1000000005']SELECT [Id] AS [cust_id] FROM(VALUES('1000000004'),('1000000005'),('1000000006'),('1000000007')) dt ([Id])INTERSECTSELECT [cust_id] FROM [Customers]

Set Operators - EXCEPT and INTERSECT

Set Operators - UNION

更多相关文章

随机推荐