Re: Is there a conditional string-concatenation ?

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