Обсуждение: Is there a conditional string-concatenation ?

  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'

On Tue, Oct 12, 2010 at 06:09:07AM +0200, Andreas wrote:
>  Hi,
> Is there a conditional string-concatenation ?

Perhaps this:

CREATE OR REPLACE FUNCTION mycat(text, text, text) RETURNS TEXT LANGUAGE sql
IMMUTABLE AS $$
SELECT CASE   WHEN $1 IS NULL OR $1 = '' THEN trim($3)   WHEN $3 IS NULL OR $3 = '' THEN trim($1)   ELSE trim($1) ||
trim(coalesce($2,'')) || trim($3)
 
END;

--
Joshua Tolley / eggyknap
End Point Corporation
http://www.endpoint.com

2010/10/12 Andreas <maps.on@gmx.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_DoeJohnDoe
JohnJohnDoe
(6 rows)

Osvaldo

Hello

more simply

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

Regards

Pavel Stehule

2010/10/12 Osvaldo Kussama <osvaldo.kussama@gmail.com>:
> 2010/10/12 Andreas <maps.on@gmx.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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