Question

我必须在表之间执行'left'或'inner'连接操作取决于我的存储过程中的输入参数。我知道如何做到这一点非常简单：

if flag = 0
begin 
 select t1.*, t2.* from t1 
 inner join t2 on t2.id=t1.id 
end
else 
begin
 select t1.*, t2.* from t1 
 left join t2 on t2.id=t1.id 
end

还有更多解决方案吗？谢谢

Answer 1

你可以通过做这样的事情只使用左连接来做到这一点

select t1.*, t2.* from t1 
 left outer join t2 on t2.id=t1.id 
WHERE flag = 1 OR t2.id IS NOT NULL

Answer 2

你没有提到这种语言，所以也许是这样的：

select t1.*, t2.* from t1 
left join t2 on t2.id=t1.id 

if flag = 0
begin 
 where t2.id is not null
end

Answer 3

 select t1.*, t2.* 
   from t1 
        inner join t2 on t2.id = t1.id 
  where flag = 0
 UNION
 select t1.*, t2.* 
   from t1 
        left outer join t2 on t2.id = t1.id
  where coalesce(flag, 1) <> 0;

左或内连接取决于参数

3 个答案: