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mysql concat

Medium Priority
Last Modified: 2012-05-07
I am using the query below to update newstreet field however if there is a null record in the concat fields then the newstreet field is null. what can I do to carry on even if one of the fields are null.(Please mysql query only. no php)
update vaddress set newstreet = Concat(pre_dir, ' ', street, ' ', stype )
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Top Expert 2008
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use CONCAT_WS('separator',field1,field2,field3) like so:
update vaddress set newstreet = Concat_WS(' ',pre_dir, street, stype );

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update vaddress set newstreet = IFNULL(Concat(pre_dir, ' ', street, ' ', stype ), '')
Or if you still want some to be retained:

update vaddress set newstreet = Concat(IFNULL(pre_dir,'<N/A>'), ' ', IFNULL(street,'<N/A>'), ' ', IFNULL(stype,'N/A'))

You use the string 'N/A' to signify that no such data inputted. In your program, you can detect such value and perform a task accordingly.
The problem with IFNULL, etc, is that you have to define that for every field, and then you end up with very unclean output results (for example, your newstreet will be full of values like 'N/A Fifth Avenue' and '145 Fifth N/A' - the cleanest solution would be to first create a field on your table called 'flagged_incomplete' and run your queries like so:
update vaddress add `flagged_incomplete` int(1) default 0 BEFORE `newstreet`;
update vaddress set `flagged_incomplete` = NULL where (is_null(pre_dir) OR is_null(street) OR is_null(stype));
// now run the query with concat_ws:
update vaddress set newstreet = Concat_WS(' ',pre_dir, street, stype );
//now, at least you can find incomplete addresses by using:
select * from vaddress where flagged_incomplete = 1;

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(sorry the first query should read as follows)
ALTER TABLE vaddress ADD `flagged_incomplete` int(1) default 0 BEFORE `newstreet`;

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A cleaner output would be:

update vaddress set newstreet = Concat(IFNULL(pre_dir,''), ' ', IFNULL(street,'''), ' ', IFNULL(stype,''))

You don't need to add another field just to check incomplete address.  The following can do the trick:

select * from vaddress where (pre_dir + street + stype) is null


select * from vaddress where pre_dir is null or street is null or stype is null
Top Expert 2005

The CONCAT_WS() that thinkingman2 showed is the cleanest approach; it avoids repeating the separator for each argument, and it quietly skips any arguments that are NULL.
hmm... ok, but i'm not sure why using coalesce would be better in this case? anybody have an answer to that?
Top Expert 2008

I don't think it is better... but it is good enough: it gets the job done. Maybe the asker just started from the top and accepted the first working solution.
makes sense!
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