根据条件选择连接表

Question

我有三张桌子

1. 表A

我需要根据传递的参数将TableA连接到TableB或TableC。ie

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

我尝试了以下查询

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

但是，这是给语法错误。有人能帮忙吗？

解决方案：

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

步骤1：创建一个包含需求列的临时表步骤2：如果paramB有一个值，则与TableB连接，否则与TableC连接。

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 2

你可以试试这样的方法：

  select *
  from a 
  left join b ON <Joining Condition>
  left join c ON <Joining Condition>
  where paramB <> '' or paramC <> ''

Answer 3

您可以使用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，表B和表C的列数和数据类型必须相同，否则会产生错误。