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  1. #1
    Atoga is offline Novice
    Windows 7 64bit Access 2013
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    Mar 2015
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    21

    How to join on fields containing nulls

    Hello Everyone,


    I need to join two tables on the SQL Server and the only field they have in common and what I can join on have many null values in each table. I would like to see all the records as a result, so I was thinking of Full Outer Join maybe. What is the best practise/what would you recommend me?
    Thanks

  2. #2
    Ajax is offline VIP
    Windows 8 Access 2010 32bit
    Join Date
    Mar 2015
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    9,444
    you can't join a null field to another field (null or not) so there is no best practice.

    you can display all the records in a table by using something like

    select * from dbotable where somefield is null

    alternative you can try something like (never tested it in a join, so may not work)

    select * from table1 inner join table2 where nz(table1.somefield,1)=nz(table2.somefield,1)

    but if you have 10 records in each table with null values, that will return 100 rows

  3. #3
    orange's Avatar
    orange is offline Moderator
    Windows XP Access 2003
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    Sep 2009
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    Ottawa, Ontario, Canada; West Palm Beach FL
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    15,769

  4. #4
    ItsMe's Avatar
    ItsMe is offline Sometimes Helpful
    Windows 8 Access 2013
    Join Date
    Aug 2013
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    7,863
    I am not an expert with Transact SQL, but I would try with a Left or Right join to start. And then, include some WHERE criteria for the Null situation. Rather than join on fields that have Nulls, can you join on another field that has unique values (Key)? And then use a where clause like ...
    WHERE ((FirstField Is Null AND [SecondField] Is Null)) OR (FirstField >"" AND [SecondField] >"")

    If you want to try a full outer, you will need to create a passthrough query or a View in SQL Server. Perhaps creating more than one JOIN would be beneficial.

Please reply to this thread with any new information or opinions.

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