Thread: PL/PGSQL beginning is hard....

hello,

i am a beginner at SQL and PL/pgsql.... and thus have some surely
already known problems...

i have set up some tables, and wanted to play around with inbuild
functions, and set up the following function:

CREATE FUNCTION balance (int4) RETURNS int4 AS '   DECLARE      compte ALIAS FOR $1;      actplus accounts.num%TYPE;
 actminus accounts.num%TYPE;      actres accounts.num%TYPE;      BEGIN          SELECT SUM(amount) INTO actplus FROM
journalWHERE plus=compte;      select sum(amount) INTO actminus from journal where minus=compte;      actres := actplus
-actminus;      RETURN actres;        END;         ' LANGUAGE 'plpgsql';
 


Now this works fine, until it hits one of the cases where either of the
selects returns an empty result (meaning that no line conforming to the
contraint could be found) in this case even if the other select returns
a value, the whole function does return nothing....

what did i wrong, or what do i have to change, to assume the value 0 if
no hit was found to the select?

BTW i am wondering if the same thing could have been achieved with sole
SQL, and if yes, how....

-- 
ciao bboett
==============================================================
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http://inforezo.u-strasbg.fr/~bboett http://erm1.u-strasbg.fr/~bboett
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the total amount of intelligence on earth is constant.
human population is growing....

> i am a beginner at SQL and PL/pgsql.... and thus have some surely
> already known problems...
> 
> i have set up some tables, and wanted to play around with inbuild
> functions, and set up the following function:
> 
> CREATE FUNCTION balance (int4) RETURNS int4 AS '
>     DECLARE
>        compte ALIAS FOR $1;
>        actplus accounts.num%TYPE;
>        actminus accounts.num%TYPE;
>        actres accounts.num%TYPE;
>        BEGIN    
>        SELECT SUM(amount) INTO actplus FROM journal WHERE plus=compte;
>        select sum(amount) INTO actminus from journal where minus=compte;
>        actres := actplus - actminus;
>        RETURN actres;
>          END;
>           ' LANGUAGE 'plpgsql';
> 
> 
> Now this works fine, until it hits one of the cases where either of the
> selects returns an empty result (meaning that no line conforming to the
> contraint could be found) in this case even if the other select returns
> a value, the whole function does return nothing....
> 
> what did i wrong, or what do i have to change, to assume the value 0 if
> no hit was found to the select?

Probably this would do it:select coalesce(sum(amount),0) ...


> BTW i am wondering if the same thing could have been achieved with sole
> SQL, and if yes, how....

You might be able to do this with subselects..(select coalesce(sum(amount), 0) from ... ) - (select coalesce...)

So, maybe something like this, if you were say going over a table which
had the compte values:select (select coalesce(sum(amount), 0) from journal where plus=compte)      -(select
coalesce(sum(amount),0) from journal where minus=compte)from table_with_compte_values;