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Combine Two Datasets

Posted on 2014-12-10
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Last Modified: 2015-01-19
Dear all,

I'm trying to combine two datasets, tables LocationData and MonitoredData based on matching values in field2 and field3.  All field types are string.  Sorry for the names I decided to make it simple to explain it.

Does the below query look like it will work?  Its not returning any results.

SELECT [LocationData].Field1, [LocationData].Field4, MonitoredData.Field2, MonitoredData.Field3 INTO MappingTable
FROM [LocationData] INNER JOIN MonitoredData ON [LocationData].Field3= MonitoredData.Field3
WHERE ((([LocationData].Field1) Is Not Null) AND ((MonitoredData.Field2)=[LocationData].Field2) AND ((MonitoredData.Field3)=[LocationData].Field3));

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Thanks
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Question by:AndyC1000
3 Comments
 
LVL 49

Expert Comment

by:Gustav Brock
ID: 40493274
It could be reduced to:

SELECT
    [LocationData].Field1,
    [LocationData].Field4,
    MonitoredData.Field2,
    MonitoredData.Field3
INTO
    MappingTable
FROM
    [LocationData],
    MonitoredData
WHERE
    [LocationData].Field1 Is Not Null
    AND
    MonitoredData.Field2 = [LocationData].Field2
    AND
    MonitoredData.Field3 = [LocationData].Field3;

/gustav
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LVL 51

Expert Comment

by:HainKurt
ID: 40494080
Its not returning any results.

of course it will not... it is inserting into some table...

remove into statement...

SELECT l.Field1, l.Field4, m.Field2, m.Field3
FROM [LocationData] l 
INNER JOIN MonitoredData m ON l.Field3= m.Field3 AND m.Field2=l.Field2 AND l.Field1 Is Not Null

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LVL 35

Accepted Solution

by:
PatHartman earned 500 total points
ID: 40494096
I would change the join to include both fields.

SELECT [LocationData].Field1, [LocationData].Field4, MonitoredData.Field2, MonitoredData.Field3 INTO MappingTable
FROM [LocationData] INNER JOIN MonitoredData ON [LocationData].Field3 = MonitoredData.Field3 AND MonitoredData.Field2 =[LocationData].Field2
WHERE [LocationData].Field1 Is Not Null;

But the suggested change is for efficiency.  It shouldn't change the result.  If the query is not returning any rows, it is because there are none that match.

To debug, I would back out one condition at a time.  So start by removing the where clause.  If that doesn't work, remove the second field in the join.  If that doesn't work, put the second field back and remove the first.

You should also examine the data.  It is possible that one table has trailing blanks or something in the columns and that will prevent the join from working.
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