Re: String Comparison and NULL

["Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com>]

Hello

2008/4/28  <seijin(at)gmail(dot)com>:
> Hi,
>
> I'm fairly new to PG and databases in general so this may very well be
> a problem in my thought process.
>
> If I have a simple table with an ID (integer) and Animal (text) like
> this...
>
> 1 Dog
> 2 Cat
> 3 NULL
> 4 Horse
> 5 Pig
> 6 Cat
> 7 Cat
>
> ... and I do something like "select id where animal <> 'Cat';"  then
> shouldn't 1, 3, 4 and 5 be picked?  As it is I only get 1, 4 and 5.
> NULL is not 'Cat'.  I realize that if I were testing for NULL itself I
> would use IS or IS NOT but this...?  I'm a little confused.
>

In this case use operator IS DISTINCT FROM

select id where animal IS DISTINCT FROM 'Cat';

Regards
Pavel Stehule

> Thanks!
>
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