Обсуждение: Concatenating multiple fetches into a single string

Dnia 2003-12-01 13:01, Użytkownik Kumar napisał:
> Dear Friends,
>  
> I am doing a migration from SQL server to Postgres SQL. A simple select 
> fetches the following names.
>  
> select full_name FROM project_members where 
> project_members.project_role_id in (' + @p_res_ids + ') ;
>  
> Let us say if the results are
>  
> full_name
> ---------------
> David
> Postgres
> plpgsql
>  
> I need to send the out put as David,Postgres,Plsql -- one string, 
> concatenates the fetches from multiple rows. This was handled in SQL 
> server with a cursor.

I can't find simpler function (if I remember well, there is such one), 
so there is my version of aggregate function you need:


create or replace function comma_aggregate(varchar,varchar) returns 
varchar as '
begin if length($1)>0 and length($2)>0 then     return $1 || '', '' || $2; elsif length($2)>0 then   return $2; end if;
return$1;
 
end;
' language 'plpgsql';

drop aggregate comma(varchar) cascade;
create aggregate comma (basetype=varchar, sfunc=comma_aggregate,
stype=varchar, initcond='' );

Regards,
Tomasz Myrta

Thanks for your reply.

But how to use this comma_aggregate( ) function to concatenate the fetched
columns values from a select statement. In my example my select stmt fetches
the following 3 rows. How can I use this function to concatenate them.

Select full_name FROM project_members where project_members.project_role_id
in ( ' x,y,z ') ;
full_name---------------DavidPostgresplpgsql

Expected return string is - 'David,Postgres,Plsql'

Regards
Kumar
----- Original Message ----- 
From: "Tomasz Myrta" <jasiek@klaster.net>
To: "Kumar" <sgnerd@yahoo.com.sg>
Cc: "psql" <pgsql-sql@postgresql.org>
Sent: Tuesday, December 02, 2003 1:31 AM
Subject: Re: [SQL] Concatenating multiple fetches into a single string


> Dnia 2003-12-01 13:01, Użytkownik Kumar napisał:
> > Dear Friends,
> >
> > I am doing a migration from SQL server to Postgres SQL. A simple select
> > fetches the following names.
> >
> > select full_name FROM project_members where
> > project_members.project_role_id in (' + @p_res_ids + ') ;
> >
> > Let us say if the results are
> >
> > full_name
> > ---------------
> > David
> > Postgres
> > plpgsql
> >
> > I need to send the out put as David,Postgres,Plsql -- one string,
> > concatenates the fetches from multiple rows. This was handled in SQL
> > server with a cursor.
>
> I can't find simpler function (if I remember well, there is such one),
> so there is my version of aggregate function you need:
>
>
> create or replace function comma_aggregate(varchar,varchar) returns
> varchar as '
> begin
>   if length($1)>0 and length($2)>0 then
>       return $1 || '', '' || $2;
>   elsif length($2)>0 then
>     return $2;
>   end if;
>   return $1;
> end;
> ' language 'plpgsql';
>
> drop aggregate comma(varchar) cascade;
> create aggregate comma (basetype=varchar, sfunc=comma_aggregate,
> stype=varchar, initcond='' );
>
> Regards,
> Tomasz Myrta
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
>       subscribe-nomail command to majordomo@postgresql.org so that your
>       message can get through to the mailing list cleanly

Dnia 2003-12-02 05:51, Użytkownik Kumar napisał:
> Thanks for your reply.
> 
> But how to use this comma_aggregate( ) function to concatenate the fetched
> columns values from a select statement. In my example my select stmt fetches
> the following 3 rows. How can I use this function to concatenate them.
> 
> Select full_name FROM project_members where project_members.project_role_id
> in ( ' x,y,z ') ;
> 
>  full_name
>  ---------------
>  David
>  Postgres
>  plpgsql
> 
> Expected return string is - 'David,Postgres,Plsql'

Where is the problem?
It's an aggregate function - you use it like the other ones:

select comma(full_name) from...

There is one problem with this function - strings order is unexpectable, 
but you can always sort them in subselect before using this function:

select comma(full_name) from
(select full_name from .... order by full_name) X;

Regards,
Tomasz Myrta