[AccessD] "Not In" query speed

John,
If you are timing queries using IN and Not IN, you may wish to try 
EXISTS and NOT Exists. We have had many queries that were just "too
slow" with IN operator that were speeded up by using Exists.

eg

SELECT claimId 
FROM tblClaim
where NOT EXISTS 
  (select "x" from  tblClaimLogged WHERE tblClaim.claimId =
tblClaimLogged.claimId)
 
Jack

-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com] On Behalf Of jwcolby
Sent: Monday, October 29, 2007 10:16 AM
To: 'Access Developers discussion and problem solving'
Subject: [AccessD] "Not In" query speed

Does anyone have any information on the speed of a "not in" query?  That
is
where an outer join to a table is used and then a filter set on the PK
(or
any field really) of the outer joined table to discover all records "not
in"
the outer joined table?

Is the speed the same as an inner join would have been?  Is there more
overhead because of the where clause?  

In other words, assume a table where there are 50K claim records in
tblClaim.  
Assume that there are 25K records in TblClaimLogged (exactly 1/2 the
number
of records in tblClaim) and that each ClaimID is only in tblClaimLogged
one
time.  

Now do an inner join to discover which records are IN tblClaimLogged.  
Now do an outer join to discover which records are NOT IN
tblClaimLogged.  

Both queries should return exactly 25K records since exactly 1/2 of the
records in tblClaim are in tblClaimLogged, and each record can only be
in
there once.

Do the two queries return the result sets in the same amount of time?

John W. Colby
Colby Consulting
www.ColbyConsulting.com 

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