Re: Interesting query outcomes

Jerry Stuckle <[email protected]> Wed, 19 Aug 2020 16:15:24 -0400

Newsgroups	comp.databases.mysql
Organization	A noiseless patient Spider
Message-ID	<[email protected]>

On 8/18/2020 4:33 PM, Joe wrote:
> I have a MySQL table field sometimes with NULL or empty values when there is no data.  When I wrote the following to count data in this field:
> 
> select CASE WHEN (TNAM is NULL || TNAM='') THEN 'default'
>                         ELSE TNAM END,  count(1)
>   from ITEMS group by 1;
> 
> I got:
> 
> | default          |     2929 |
> | default          |      139 |
> | item A           |      347 |
> | item B           |      831 |
> ....
> -- why "default" repeats? I humble one is from "TNAM is NULL" and the other from "TNAM=''", and also thought they should have been combined with "group" function... Thoughts without actually update table to turn "empty" to NULL or vise versa?
> 
> Joe
> 

My quest would be the GROUP BY clause is being applied before the CASE 
WHEN clause.


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Jerry Stuckle
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