Merge简介
SQL Server 2008提供了一个增强的SQL命令Merge。它的功能是根据与源表联接的结果,对目标表执行插入、更新或删除操作。例如,根据在另一个表中找到的差异在一个表中插入、更新或删除行,可以对两个表进行同步。
Merge用法
语法
[ WITH <common_table_expression> [,...n] ]
MERGE
[ TOP ( expression ) [ PERCENT ] ]
[ INTO ] <target_table> [ WITH ( <merge_hint> ) ] [ [ AS ] table_alias ]
USING <table_source>
ON <merge_search_condition>
[ WHEN MATCHED [ AND <clause_search_condition> ]
THEN <merge_matched> ] [ ...n ]
[ WHEN NOT MATCHED [ BY TARGET ] [ AND <clause_search_condition> ]
THEN <merge_not_matched> ]
[ WHEN NOT MATCHED BY SOURCE [ AND <clause_search_condition> ]
THEN <merge_matched> ] [ ...n ]
[ <output_clause> ]
[ OPTION ( <query_hint> [ ,...n ] ) ]
;
<merge_matched>::=
{ UPDATE SET <set_clause> | DELETE }
<merge_not_matched>::=
{
INSERT [ ( column_list ) ]
{ VALUES ( values_list )
| DEFAULT VALUES }
}
<output_clause>::=
{
[ OUTPUT <dml_select_list> INTO { @table_variable | output_table }
[ (column_list) ] ]
[ OUTPUT <dml_select_list> ]
}
<clause_search_condition> ::=
{ [ NOT ] <predicate> | ( <search_condition> ) }
[ { AND | OR } [ NOT ] { <predicate> | ( <search_condition> ) } ]
[ ,...n ]
示例
假如,有一总产品列表,一个分店产品列表,需要从分店添加产品时更新总产品列表。总产品表,分店产品表结构完全一致:
-- 总产品列表
Create table Demo_AllProducts
(PKID int not null identity(1,1) primary key,
DName Nvarchar(20) null,
DCode NVarchar(30) null,
DDate datetime null)
-- 向表中插入数据
Insert into Demo_AllProducts (DName,DCode,DDate)
values
('DemoA','AAA',GETDATE()),
('DemoB','BBB',GETDATE()),
('DemoC','CCC',GETDATE()),
('DemoD','DDD',GETDATE()),
('DemoE','EEE',GETDATE())
-- 分店产品列表
Create table Demo_Shop1_Product
(PKID int not null identity(1,1) primary key,
DName Nvarchar(20) null,
DCode NVarchar(30) null,
DDate datetime null)
Insert into Demo_Shop1_Product (DName,DCode,DDate)
values
('DemoA','AAA',GETDATE()),
('DemoB','CCC',GETDATE()),
('DemoF','FFF',GETDATE())
假定现在需要将分店数据完全合并到总产品表中,以编码字段为依据。如果产品名称不一致,则用分店的产品名称替换总产品名称;如果总产品表中不存在,则添加;如果分店表中不存在,则从总产品表中删除分店中没有的行。实现语句如下:
--确定目标表
Merge Into Demo_AllProducts p
--从数据源查找编码相同的产品
using Demo_Shop1_Product s on p.DCode=s.DCode
--如果编码相同,则更新目标表的名称
When Matched and P.DName<>s.DName Then
Update set P.DName=s.DName
--如果目标表中不存在,则从数据源插入目标表
When Not Matched By Target Then
Insert (DName,DCode,DDate) values (s.DName,s.DCode,s.DDate)
--如果数据源的行在源表中不存在,则删除源表行
When Not Matched By Source Then Delete;
此时,执行完成后,两个表的行均如下:
--PKID DName DCode DDate
--1 DemoA AAA 2010-10-17 20:31:00.827
--2 DemoB CCC 2010-10-17 20:31:00.827
--3 DemoF FFF 2010-10-17 20:31:00.827
如果需要记录Merge语句影响的行,可以用Output子句,如果仅仅需要知道影响的行数,可以使用@@ROWCOUNT或ROWCOUNT_BIG(),修改后的示例如下:
--定义表变量以存储输出
Declare @tableVarRecord Table
(MPKID int not null identity(1,1) primary key
,PKID int null
,DName Nvarchar(20) null
,DCode NVarchar(30) null
,DDate datetime null
)
--确定目标表
Merge Into Demo_AllProducts p
--从数据源查找编码相同的产品
using Demo_Shop1_Product s on p.DCode=s.DCode
--如果编码相同,则更新目标表的名称
When Matched and P.DName<>s.DName Then
Update set P.DName=s.DName
--如果目标表中不存在,则从数据源插入目标表
When Not Matched By Target Then
Insert (DName,DCode,DDate) values (s.DName,s.DCode,s.DDate)
--如果数据源的行在源表中不存在,则删除源表行
When Not Matched By Source Then
Delete OUTPUT deleted.* INTO @tableVarRecord;
----Delete OUTPUT Inserted.* INTO @tableVarRecord;
--返回上个Merge语句影响的行数
select @@ROWCOUNT as Count1,ROWCOUNT_BIG() as Count2
select * from @tableVarRecord;
结果:
-影响的行数
--Count1 Count2
--5 5
--Deleted表的行
--MPKID PKID DName DCode DDate
--1 NULL NULL NULL NULL
--2 2 DemoB BBB 2010-10-17 21:42:30.700
--3 3 DemoC CCC 2010-10-17 21:42:30.700
--4 4 DemoD DDD 2010-10-17 21:42:30.700
--5 5 DemoE EEE 2010-10-17 21:42:30.700