Re: pl/pgsql loop thru columns names

2009/8/19 Dilyan Berkovski <berkovski(at)yahoo(dot)com>:
> Hi All,
>
> I have a nasty table with many repeating columns of the kind port_ts_{i}_<something>, where {i} is from 0 to 31, and <something> could be 3 different words.
> I have made a pl/pgsql function that checks those columns from port_ts_1_status to port_ts_31_status and counts something, however this is nasty and ugly thing to do - repeat 31 times one statement for looping thru {i} and do it 3 times to loop thru <something>. This is how I do it now:
> REATE OR REPLACE FUNCTION auto_util()
>  RETURNS "trigger" AS
> $BODY$DECLARE
> count_free      integer;
> util            real;
> BEGIN
> count_free = 0;
> IF new.port_ts_1_status='free' THEN count_free = count_free + 1;
> End if;
> IF new.port_ts_2_status='free' THEN count_free = count_free + 1;
> End if;
> IF new.port_ts_3_status='free' THEN count_free = count_free + 1;
> End if;
> IF new.port_ts_4_status='free' THEN count_free = count_free + 1;
> End if;
> IF new.port_ts_5_status='free' THEN count_free = count_free + 1;
> End if;
> IF new.port_ts_6_status='free' THEN count_free = count_free + 1;
> End if;
> IF new.port_ts_7_status='free' THEN count_free = count_free + 1;
> End if;
> .... and till the end ilke this.
>
> Can I do a loop, and make the column naming to be build dynamically (as the dynamic queries in pl/pgsql)?
> something like
> for i in 1..31 do
> Loop
> If new.port_ts_[i]_status='free' ... and so on
> end Loop.
> I tryed but unsuccessfully :(, and can not find much in the documentation.
> I am using 8.1 and 8.2 Postgresql DBs.
> Someone with an idea?

yes - on this versions, you have to use dynamic pl languages as plperl
or pltcl. On 8.4 you can do it in plpgsql too.

http://okbob.blogspot.com/2008/06/execute-using-feature-in-postgresql-84.html

regards
Pavel Stehule

> Thanks
>
>
>
>
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