Sql Server多表查询

1. 同库操作
   select a.列名1,b.列名2,a.列名3 from 表名1 as a
   join 表名2 as b
   on a.关联字段=b.关联字段 

2. 不同库操作
   select a.列名1,b.列名2,a.列名3 from 库名1.dbo.表名1 as a
   join 库名2.dbo.表名2 as b
   on a.关联字段=b.关联字段 

3. 2张表以上的多表连接：先两张连接再与第三张连接，依次下去，如
   select a.列名1,b.列名2,a.列名3 from 表名1 as a
   join 表名2 as b
   on a.关联字段=b.关联字段
   join 表名3 as c
   on a.关联字段=c.关联字段