根据不同的条件查询不同的表sql

/*
user_ID name
----------- --------------------------------------------------
1
a1
2
a2
user_ID name
----------- --------------------------------------------------
1
a1
2
b2
*/
select * from ta select * from tb select * from tc
--方法一
select c.[user_id],name=case user_type when 'a' then when 'b' then end from tc c,ta a,tb b where a.[user_id]=c.[user_id] and b.[user_id]=c.[user_id]
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/* a表 er_id b表 er_id c表 er_id er_type
根据不同的条件查询不同的表 sql
当c表的 er_type = "a" 时 它显示 a表的 当c表的 er_type = "b" 时 它显示 b表的 a,b,c表中的 er_id = er_id,er_id = er_id1b12 Nhomakorabeab2
user_ID user_type
----------- --------------------------------------------------
1
a
2
b
user_id 输出
----------- --------------------------------------------------
--方法二
SELECT FROM
er_ID, CASE user_type WHEN 'a' THEN WHEN 'b' THEN END AS 输出 tc INNER JOIN ta ON er_ID = er_ID INNER JOIN tb ON er_ID = er_ID
*/
if object_id('ta')is not null drop table ta
go create TABLE ta([user_ID] int,name varchar(50)) INSERT INTO ta select 1,'a1' union all select 2,'a2'
if object_id('tb')is not null drop table tb
go create TABLE tb([user_ID] int,name varchar(50)) INSERT INTO tb select 1,'b1' union all select 2,'b2'
if object_id('tc')is not null drop table tc
go create TABLE tc([user_ID] int,user_type varchar(50)) INSERT INTO tc select 1,'a' union all select 2,'b'