I have the following function(s) that each joins an active record with
it's most recent record in an audit trail table, to show differences.
I've perused the execution plans for 2 versions of this function in QA
and it seems to me that the two versions execute identically - that is,
the addressing the sub-query of the WHERE clause with either IN or =
results in the same execution plan.
Does this seem plausible or did I misinterpret something in QA?
---
ALTER FUNCTION Function9()
RETURNS TABLE
AS RETURN
(
SELECT ID, Numb, Name, Q.Diff_ID, Q.Diff_Numb, Q.Diff_Name,
FROM tblQuestion INNER JOIN
(
SELECT ID AS Diff_ID, Numb AS Diff_Numb, Name as Diff_Name
FROM tblQuestion_Audit
WHERE AuditDate IN (SELECT MAX(AuditDate) FROM tblQuestion_Audit)
) AS Q
ON dbo.tblItem.ID = Q.Diff_ID
)
ALTER FUNCTION Function10()
RETURNS TABLE
AS RETURN
(
SELECT ID, Numb, Name, Q.Diff_ID, Q.Diff_Numb, Q.Diff_Name,
FROM tblQuestion INNER JOIN
(
SELECT ID AS Diff_ID, Numb AS Diff_Numb, Name as Diff_Name
FROM tblQuestion_Audit
WHERE AuditDate = (SELECT MAX(AuditDate) FROM tblQuestion_Audit)
) AS Q
ON dbo.tblItem.ID = Q.Diff_ID
) 3 1889
Beowulf (be*****************@hotmail.com) writes: I have the following function(s) that each joins an active record with it's most recent record in an audit trail table, to show differences. I've perused the execution plans for 2 versions of this function in QA and it seems to me that the two versions execute identically - that is, the addressing the sub-query of the WHERE clause with either IN or = results in the same execution plan.
Does this seem plausible or did I misinterpret something in QA?
It seems very plausible.
I nevertheless prefer the version with =. But that is merely because
it's easier to read and understand.
--
Erland Sommarskog, SQL Server MVP, es****@sommarskog.se
Books Online for SQL Server 2005 at http://www.microsoft.com/technet/pro...ads/books.mspx
Books Online for SQL Server 2000 at http://www.microsoft.com/sql/prodinf...ons/books.mspx
Erland Sommarskog wrote: Beowulf (be*****************@hotmail.com) writes: I have the following function(s) that each joins an active record with it's most recent record in an audit trail table, to show differences. I've perused the execution plans for 2 versions of this function in QA and it seems to me that the two versions execute identically - that is, the addressing the sub-query of the WHERE clause with either IN or = results in the same execution plan.
Does this seem plausible or did I misinterpret something in QA? It seems very plausible.
So, the SQL Server query optimizer is smart enough to figure out that
the sub-query in the WHERE clause will return only a single value and is
able to figure out that WHERE x IN (a) is the same as WHERE x = a.
That's pretty cool.
I nevertheless prefer the version with =. But that is merely because it's easier to read and understand.
Thanks for the input. I certainly agree. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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