mssql如何提高数据库关联查询性能

--> 测试数据：[a1]
if object_id('[a1]') is not null drop table [a1]
create table [a1]([id] int,[sortid1] int,[sortid2] int,[info] varchar(5))
insert [a1]
select 1,1,3,'info' union all
select 2,2,4,'info2'

--> 测试数据：[b2]
if object_id('[b2]') is not null drop table [b2]
create table [b2]([sortid] int,[name] varchar(5))
insert [b2]
select 1,'分类1' union all
select 2,'分类2' union all
select 3,'分类3' union all
select 4,'分类4'

select * from [a1]
select * from [b2]

select a1.id,sortid1,b2.name,a1.sortid2,b.name,a1.[info]
from dbo.a1
left join b2 on a1.sortid1 = b2.sortid
left join b2 b on a1.sortid2 = b.sortid

/*
id sortid1 name sortid2 name info
----------- ----------- ----- ----------- ----- -----
1 1 分类1 3 分类3 info
2 2 分类2 4 分类4 info2

(2 行受影响)
*/

原始方法

select id,rortid1,b.name as name1 , sortid2,c.name as name2,info
from a left join b on a.rortid1=b.rortid
left join b c on a.rortid2=b.rortid

比较实用的方法

视图可以简化操作，不能提高性能。可以尝试建立索引视图