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Query to find delta / exceptions between 2 tables

Posted on 2014-12-04
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Last Modified: 2014-12-04
I have two tables (tableA, tableB) which basically contain the same data.  The key between the 2 is serial_number.  I need a query to return the delta between the 2 tables.

TableA contains all the data that should be in TableB but that is not the case.  I need to determine which serial numbers from TableA are not appearing in TableB.
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Question by:szadroga
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14 Comments
 
LVL 15

Expert Comment

by:Haris Djulic
ID: 40480722
Hello,

try to use EXCEPT command..
SELECT *
FROM Table A
EXCEPT
SELECT *
FROM TableB

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LVL 24

Expert Comment

by:Phillip Burton
ID: 40480738
SELECT serial_number
FROM tableA
EXCEPT
SELECT serial_number
FROM tableB
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Author Comment

by:szadroga
ID: 40480744
great, so is that basically a translation of

select * from TableA where SERIAL_NUMBER does not equal (select serial_number from TableB);
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Author Comment

by:szadroga
ID: 40480760
I want to return more fields in the query, not just serial_number but serial_number is the field I need to base the "delta" logic on.
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LVL 24

Expert Comment

by:Phillip Burton
ID: 40480768
I don't think either of ours are that exactly.

Haris compares the entirety of all of the fields, and only where all the fields are identical in both tables for a particular row, then exclude that.

Mine shows only the serial_number, and excludes tableB's serial numbers; it doesn't show all the fields.

If you want to show everything (as you have said "Select *"), then

select * from TableA where SERIAL_NUMBER not in (select serial_number from TableB);
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LVL 48

Accepted Solution

by:
Vitor Montalvão earned 500 total points
ID: 40480781
I prefer the NOT EXISTS clause:
SELECT *
FROM TableA
WHERE NOT EXISTS (SELECT 1 
              FROM TableB
              WHERE TableB.serial_number=TableA.serial_number)

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LVL 35

Expert Comment

by:PatHartman
ID: 40480861
Or, you can use a left join.
Select *
From tblA Left Join tblB On tblA.SerialNumber = tblB.SerialNumber
Where tblB.SerialNumber is Null;

"EXCEPT" is not valid Access SQL Syntax.
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Author Comment

by:szadroga
ID: 40480884
Vitor,

What does the SELECT 1 represent in the sub SELECT query?
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LVL 48

Expert Comment

by:Vitor Montalvão
ID: 40480925
SELECT clause needs at least a column or value. 1 is a constant value so it's used to avoid access to data. It's an old trick ;)
Could be SELECT NULL or SELECT 'A' or any constant value. It's better than a SELECT * since you won't need the sub-query to return any data.
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Author Comment

by:szadroga
ID: 40480928
thanks for clarifying.  I will keep that trick in mind going forward.
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LVL 45

Expert Comment

by:aikimark
ID: 40481227
Is the data in an Access database or a SQL Server database?  If an Access, the EXCEPT keyword is not supported. (confirmed Pat's comment)

You can do this in a single UNION query.
Example:
Select tblA.*, "In A Not In B" As tblDiff
From tblA Left Join tblB On tblA.SerialNumber = tblB.SerialNumber
Where tblB.SerialNumber is Null
UNION ALL
Select tblB.*, "In B Not In A" As tblDiff
From tblB Left Join tblA On tblA.SerialNumber = tblB.SerialNumber
Where tblA.SerialNumber is Null
UNION ALL
Select tblA.*, "Field difference" As tblDiff
From tblA Join tblB On tblA.SerialNumber = tblB.SerialNumber
Where tblA.Field1 <> tblB.Field1
OR tblA.Field2 <> tblB.Field2
OR tblA.Field3 <> tblB.Field3
OR tblA.Field4 <> tblB.Field4

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Author Comment

by:szadroga
ID: 40481329
Currently in Access, but I will move to SQL if the report i am building seems beneficial.
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LVL 35

Expert Comment

by:PatHartman
ID: 40481340
The suggestion I made of the outer join and the suggestion of Not Exists will work in both variants of SQL.  But if you are going to use T-SQL (with a pass-through query) you also have the option of "EXCEPT".
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Author Closing Comment

by:szadroga
ID: 40481429
worked perfectly and at an optimal speed.
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