Re: CONCAT returns null

On 02/28/2016 02:30 AM, Andreas Kretschmer wrote:
> Sterpu Victor <victor@caido.ro> wrote:
>
>> Hello
>>
>> I have this concat:
>> CONCAT(f.nrfo, '/', TO_CHAR(fd1.validfrom, 'YYYY-MM-DD'), f2.nrfo, TO_CHAR
>> (fd7.validfrom, 'YYYY-MM-DD'), DATE(fd5.validto)-DATE(fd1.validfrom))
>> that works fine but when I change to this(I added a ' with '):
>> ARRAY_AGG(CONCAT(f.nrfo, '/', TO_CHAR(fd1.validfrom, 'YYYY-MM-DD'), ' with ',
>> f2.nrfo, TO_CHAR(fd7.validfrom, 'YYYY-MM-DD'), DATE(fd5.validto)-DATE
>> (fd1.validfrom))) AS temp,
>> then concat returns NULL.
>> Why? I tried to add ' with '::VARCHAR and ' with '::TEXT but the result is
>> still NULL.
>>
>> Thank you
>
> NULL concat with a value returns NULL. You can avoid that using
> COALESCE(value, ''), that returns the value, or, if the value NULL, ''.


http://www.postgresql.org/docs/9.5/interactive/functions-string.html
"
concat(str "any" [, str "any" [, ...] ])     text     Concatenate the text
representations of all the arguments. NULL arguments are ignored.
"
>
>
> Andreas
>


--
Adrian Klaver
adrian.klaver@aklaver.com