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From: Jonathan Moules <jonathan-lists@lightpear.com>
To: Achilleas Mantzios <achill@matrix.gatewaynet.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Always getting back a row, even with no results
Date: Fri, 11 Aug 2017 16:30:35 +0100
Message-ID: <15dd1ea396c.10c78e843106370.6070220804472515174@lightpear.com> (raw)
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Do smth like along the lines (might want to add additional code for ordering, this just happens to run correctly) :
 select * from my_table where cat = 500 UNION select null,null LIMIT CASE WHEN (select count(*) from my_table where cat=500)&gt;0 THEN (select count(*) from my_table where cat=500) ELSE 1 END ;
 Of course you can write a function to do that for you, but what made you want this in the first place? Maybe this is bad design ?



Unfortunately this is a constraint of the environment; not good design, but SQL seems like it should be the simplest place to solve this.

I tried your example; it seems the ordering is required, otherwise the results always include the null. So the below works for anyone who finds this in the future. Thanks


select
            id
from
            my_table
where
            cat = 2
 
UNION
 
select
            null as id
ORDER BY
            id ASC
LIMIT
    CASE
            WHEN (
                select
                        count(*)
                from
                        my_table
                where
                        cat = 2
                ) &gt; 0
            THEN (
                select count(*) from my_table where cat=2
                )
            ELSE
                1
    END;

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  Subject: Re: Always getting back a row, even with no results
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