Re: Is there a conditional string-concatenation ?

Hello

more simply

postgres=# CREATE OR REPLACE FUNCTION public.foo(a text, b text, c text)
RETURNS text
LANGUAGE sql
AS $function$
SELECT coalesce($1 || $2 || $3,
$1 || $2,
$2 || $3)
$function$

Regards

Pavel Stehule

2010/10/12 Osvaldo Kussama <osvaldo(dot)kussama(at)gmail(dot)com>:
> 2010/10/12 Andreas <maps(dot)on(at)gmx(dot)net>:
>>  Hi,
>> Is there a conditional string-concatenation ?
>>
>> I'd like to have an elegant way to connect 2 strings with some 3rd element
>> between only if there really are 2 strings to connect.
>>
>> e.g.
>> MyCat ( 'John', '_', 'Doe' ) --> 'John_Doe'
>> while
>> MyCat ( 'John', '_', '' ) --> 'John'
>> MyCat ( '', '_', 'Doe' ) --> 'Doe'
>> MyCat ( '', '_', '' ) --> NULL
>>
>> It should treat  NULL  and  ''  equally as empty
>> and it should trim each of the 3 elements.
>>
>> so
>> MyCat ( '       John     ', '_', NULL ) --> 'John'
>> MyCat ( 'John', NULL, 'Doe' ) --> 'JohnDoe'
>>
>
>
> Try:
> bdteste=# SELECT nullif(ltrim(rtrim(coalesce(c1,'') || coalesce(c2,'')
> || coalesce(c3,''),' _'),' _'),'')
> bdteste-#   FROM (VALUES ('John', '_', 'Doe'),('John', '_', ''),('',
> '_', 'Doe'),('', '_', ''),('       John     ', '_', NULL),('John',
> NULL, 'Doe')) AS foo(c1,c2,c3);
>  nullif
> ----------
>  John_Doe
>  John
>  Doe
>
>  John
>  JohnDoe
> (6 rows)
>
> Osvaldo
>
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