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SQL JOINS in Access

Posted on 2008-06-23
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Last Modified: 2013-11-05
I have a small SQL query. This is the SQL at the moment:

"SELECT tblClass.ClassID, tblClass.Subject, tblClass.Teacher,
sum(iif (datepart('ww',tblHomework.DateSet)=(datepart('ww',Date())) ,1,0)) as wk1,
sum(iif (datepart('ww',tblHomework.DateSet)=(datepart('ww',Date())-1) ,1,0)) as wk2,
sum(iif (datepart('ww',tblHomework.DateSet)=(datepart('ww',Date())-2) ,1,0)) as wk3,
sum(iif (datepart('ww',tblHomework.DateSet)=(datepart('ww',Date())-3) ,1,0)) as wk4
FROM tblClass LEFT JOIN tblHomework ON tblClass.ClassID = tblHomework.ClassID
WHERE (tblHomework.TaskType = 'HW' AND Subject='" & Request("Faculty") & "')
GROUP BY tblClass.ClassID, tblClass.Subject, tblClass.Teacher"

It works just fine except for one thing. tblClass contains all the classes in the school. I want all the classes to show even if they are not found in tblHomework. Basically the SQL should count the number of homeworks set for each class. If the class does not appear in tblHomework that would imply no homework has been set.

I have fiddled about with RIGHT JOIN and LEFT join but the output is the same. It only shows the classes that can be matched in both tables. I am using Access so FULL OUTER JOIN is not acceptable.

Any ideas how to solve this one?

Thanks,

Desi
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Question by:DesiMck
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3 Comments
 
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Accepted Solution

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Daniel Wilson earned 125 total points
ID: 21848289
Your WHERE clause is limiting you to rows that match.

Try this:

WHERE ((tblHomework.TaskType is NULL or tblHomework.TaskType = 'HW') AND (Subject IS NULL or Subject='" & Request("Faculty") & "'))

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Expert Comment

by:msfletch
ID: 21848290
Desi,

I believe the problem is in your WHERE clause. Even thought you are LEFT joining the tables, your WHERE clause is requesting only records that contain tblHomework.TaskType = 'HW'. This will limit your results from the tblClass table.
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Author Closing Comment

by:DesiMck
ID: 31469851
Thank you - that was very useful and well explained.  Cheers,  Desi
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