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)
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--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)
UNION
SELECT FC FROM ( VALUES ( 'a' ),( 'b' ),( 'c' ),( 'd' )) Table2 (FC)
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2.UNION ALL
(简单合并两个查询结果集,不删除重复行)
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--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 ALL
SELECT * FROM ( VALUES ( 'a' , 'Anna' ),( 'b' , 'Bob' ),( 'c' , 'Cassie' ),( 'd' , 'David' )) Table2 (FC, Name )
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3.EXCEPT
(返回出现在第一个结果集但不出现在第二个结果集中的所有行)
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--返回结果为:[e]
SELECT FC FROM ( VALUES ( 'a' ),( 'b' ),( 'c' ),( 'e' )) Table1 (FC)
EXCEPT
SELECT FC FROM ( VALUES ( 'a' ),( 'b' ),( 'c' ),( 'd' )) Table2 (FC)
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4.INTERSECT
(返回第一个查询结果集和第二个查询结果集共有的部分)
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--返回结果为:[a,b,c]
SELECT FC FROM ( VALUES ( 'a' ),( 'b' ),( 'c' ),( 'e' )) Table1 (FC)
INTERSECT
SELECT FC FROM ( VALUES ( 'a' ),( 'b' ),( 'c' ),( 'd' )) Table2 (FC)
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集合运算的使用场景
1.使用UNION
代替Where
子句中的OR
,查询速度更快
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--使用Where子句 + OR
SELECT name , population, area FROM world WHERE area > 3000000 OR population > 25000000
--使用UNION
SELECT name , population, area FROM world WHERE area > 3000000
UNION
SELECT name , population, area FROM world WHERE population > 25000000
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2.使用EXCEPT
和INTERSECT
, 过滤出列表中不存在/存在于数据库中的项
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 |
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--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])
EXCEPT
SELECT [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])
INTERSECT
SELECT [cust_id] FROM [Customers]
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--对于SQLServer 2008以前的版本
SELECT [Id] AS [cust_id] FROM
(
SELECT '1000000004' UNION ALL
SELECT '1000000005' UNION ALL
SELECT '1000000006' UNION ALL
SELECT '1000000007'
) dt ([Id])
INTERSECT
--EXCEPT
SELECT [cust_id] FROM [Customers]
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//使用C#动态生成SQL语句
var list = new List<string>(){ "1000000004" , "1000000005" , "1000000006" , "1000000007" };
string sqlQuery = string.Format($@ "
SELECT [Id] AS [cust_id] FROM
(
VALUES('{string.Join(" '),( '", list)}' )
) dt ([Id]
INTERSECT
--EXCEPT
SELECT [cust_id] FROM [Customers]"
);
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更多参考
Set Operators - EXCEPT and INTERSECT
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原文链接:https://www.cnblogs.com/makesense/p/13456100.html