在联接中使用表值函数

Question

There is a Table valued function which gives multiple rows as output and there are 2 columns as output.

Now I want use this function in the query for all the employees in the employees table

I am using CROSS APPLY but its taking long time and doesn't give any result.

This is the query which I tried

select *
from emp A Cross APPLY fnempDiv(A.EmpID)

Answer 1

I am using CROSS APPLY

• its taking long time

Unfortunately, that's the nature of CROSS APPLY, since it is a row-by-row operator. It works great for a few employee rows (convenient) but from what you describe, you should avoid it for this query and expand the query in the APPLY to the outer query. A simple INNER JOIN should do.

• doesn't give any result.

CROSS APPLY removes emp A records that don't produce any rows from the APPLY. OUTER APPLY will keep the emp A records. If you are getting 0 records overall, you might have passed the wrong column, eg A.EmpID is not the correct key.

If the function is defined like this (from your comment):

CREATE FUNCTION dbo.fnempDiv(@EmpID)
RETURNS TABLE AS RETURN
 SELECT A.EmpID,D.Name
 FROM empdetail A
 INNER JOIN empdiv D on A.empID=D.ID
 where EXISTS (select * from X)
GO

It makes no sense at all. Select * from X either fails the entire query or becomes a dud condition, simply by having a record in X or otherwise. The input parameter @EmpID is also not being used.

On the other hand, if it is declared as follows:

CREATE FUNCTION dbo.fnempDiv(@EmpID)
RETURNS TABLE AS RETURN
 SELECT A.EmpID,D.Name
 FROM empdetail A
 INNER JOIN empdiv D on A.empID=D.ID
 where A.EmpID = @EmpID
GO

Then your full query can be rewritten

select E.*, A.emp_ID as EmpDetail_Emp_ID, D.Name
from emp E
INNER JOIN empdetail A ON E.emp_ID=A.EMP_ID
INNER JOIN empdiv D on A.empID=D.ID

Moreover, the join A.empID=D.ID doesn't even look right.