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T_SQL: joining tables on nvarchar and int columns

Posted on 2013-06-03
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Last Modified: 2013-06-07
We'd like to join 2 tables on common column and get the data from both of them. The problem is that even though the data in the columns is similar, the datatype is not the same. One is nvarchar and the other is int. Some data cannot be converted to int.
What is the best way to write the query in order to get matching rows from both tables?
Thank you in advance.
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Question by:quasar_ee
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Accepted Solution

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Anthony Perkins earned 500 total points
ID: 39217666
Something like this:
FROM    TableA a
        INNER JOIN TableB b ON CASE PATINDEX('%[^0-9]%', a.nvarcharcolumn)
                                 WHEN 0 THEN CAST(a.nvarcharcolumn AS int)
                                 ELSE NULL
                               END = b.integercolumn 

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Don't use ISNUMERIC() that is a bad idea.
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Expert Comment

by:sarabhai
ID: 39217992
convert both to the nvarchar is then best because to convert int error occurs
use CAST or convert both data types to nvarchar.
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LVL 48

Expert Comment

by:PortletPaul
ID: 39217998
You could try in the other direction, i.e. convert int to nvarchar which should always work thus avoiding the patindex. (Mind you it's a pity you have to do this at all.)

select
*
from TableA a
inner join TableB b on a.nvarcolumn = convert(nvarchar,b.intcolumn)

which of these 2 columns is indexed? maximizing use of indexes may influence the choice you make.
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LVL 21

Expert Comment

by:Alpesh Patel
ID: 39225516
CAST the NVarchar column to Int or CAST INT to NVARCHAR in where or Join (ON part).

It will work for you.
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