Question

MySQL Function Problem

Asked by: djcheeky

Hi

I have created a function called GetContentCategories which gets a list of categories that are linked to a content record.

For example, if I run the following SQL:

SELECT *,GetContentCategories(contentId) from content
where '2' in (GetContentCategories(contentId))

As you can see, I am returning all content items that have a categoryList that contains category 2.

So far so good.

If I try and run that SQL when there is only ONE category returned by GetContentCategories(contentId) then this query works fine.
For example:
SELECT *,GetContentCategories(contentId) from content
where 2 in (2)        

But, if there are more than one categories linked to the content item and more than one category id is returned by calling GetContentCategories(contentId), then the query returns no records. For example:
SELECT *,GetContentCategories(contentId) from content
where 2 in (2,3,6)        

As you can see, there are 3 integer values returned by the function. 2 is clearly in the list, yet the query returns no records??

BUT - and here's the strange part, if i manually type in the values for the IN statement, then it works. In other words:

WORKS:
SELECT *,GetContentCategories(contentId) from content
where 2 in (2,3,6)      

DOESN'T WORK:
SELECT *,GetContentCategories(contentId) from content
where 2 in (GetContentCategories(contentId))

(where GetContentCategories(contentId) returns 2,3,6

What am I missing here. Manually typing in the values works, but using a function to generate the values does not. Yet the value returned by the function is EXACTLY the same as that typed manually - I have double checked!

CREATE DEFINER=`root`@`%` FUNCTION `GetContentCategories`(in_contentId BIGINT) RETURNS varchar(1024) CHARSET latin1
BEGIN
  DECLARE out_categoryList VARCHAR(1024);
  SET out_categoryList = (SELECT (CAST(GROUP_CONCAT(categoryId) AS CHAR(10000) CHARACTER SET utf8)) AS contentCategories FROM contentToCategory where contentId = in_contentId);
  RETURN out_categoryList;
END

                                  
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Asked On
2009-08-26 at 12:10:10ID24684319
Tags

MySQL

Topic

MySQL Server

Participating Experts
1
Points
125
Comments
5

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Answers

 

by: nemws1Posted on 2009-08-26 at 12:58:31ID: 25191595

I would think what you have would work as well.

I'm not duplicating what you're getting exactly (I'm getting *one* row back, not zero), but it still isn't working the way I would think.

I'm still working on it, though. ;-)

 

by: nemws1Posted on 2009-08-26 at 13:12:24ID: 25191742

Ah.  Your return result is being strictly interpreted as a single string, which I can reproduce with this (note the double quotes around the list):

SELECT *,GetContentCategories(contentId) from content
where 2 in ("2,3,6");


Now... to get rid of that.

 

by: nemws1Posted on 2009-08-26 at 13:38:43ID: 25192007

How about this?

SELECT *
FROM content
WHERE FIND_IN_SET(contentid, GetContentCategories(3))
;
                                              
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by: nemws1Posted on 2009-08-26 at 13:45:42ID: 25192080

I'm also assuming that your problem is more complex than you're presenting here.  Otherwise we could just use a Sub-select:

SELECT *
FROM content
WHERE contentid IN
  (SELECT categoryId
    FROM contentToCategory
    WHERE contentId = 3
  )
;

                                              
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by: djcheekyPosted on 2009-08-26 at 20:41:07ID: 25194405

Hi nemws1

Yes, it was a bit more complex which is why I could not use sub selects.

But you have solved the problem with FIND_IN_SET!!! Thank you.

It makes sense that because the result of the function was defined as a string that it would surrounded in quotes. Which is why it would work when one value was returned by the function but not more than one!

It was obviously just not showing the quotation marks in the Query Browser when I executed the query.

But now it works perfectly using:

SELECT *,GetContentCategories(contentId) from content
where FIND_IN_SET(2, GetContentCategories(contentId))

Thanks - that really had me scratching my head!! Now to just figure out how to force my MySQL Query  Browser to show those quotation marks in future - but that's a separate topic :)

20120131-EE-VQP-002

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