根据条件选择连接表

Question

我有3张桌子

1. 表A
2. 表B
3. 表C

我需要根据传递的参数将TableA连接到TableB或TableC.即

select * from 
TableA A 
join (TableB on <Joining Condition> /  TableC on <joining condition> )

我试过以下查询

select * from 
TableA A 
join (
   case when paramB<>'' then TableB on <Joining Condition>
   case when paramC<>'' then TableC on <joining condition>
 )

但是,这会给出语法错误.任何人都可以帮忙吗？

解:

create table #temp (<columns>)
if paramB<>''
begin
   select * from 
   TableA A 
   join TableB on <Joining Condition>
end
else if paramB<>''
begin
  select * from 
   TableA A 
   join TableC on <Joining Condition>
end

Answer 1

你可以用UNION ALL.

select *
from a
join TableB on <join condition>
where paramB <> ''

union all

select *
from a
join TableC on <join condition>
where paramC <> ''

请注意,TableB并且TableC必须具有相同数量的列并具有相同的数据类型,否则将产生错误.