Re: array_agg() NULL Handling

2010/9/1 Tom Lane <tgl@sss.pgh.pa.us>:
> Pavel Stehule <pavel.stehule@gmail.com> writes:
>> 2010/9/1 Tom Lane <tgl@sss.pgh.pa.us>:
>>> Well, you can build your own version of array_agg with the same
>>> implementation, except you mark the transition function as strict ...
>
>> I am checking this now, and it is not possible - it needs a some
>> initial value and there isn't possible to set a "internal" value.
>
> Well, you can cheat a bit ...
>
> regression=# create or replace function array_agg_transfn_strict(internal, anyelement) returns internal as
'array_agg_transfn'language internal immutable; 
> CREATE FUNCTION
> regression=# create aggregate array_agg_strict(anyelement) (stype = internal,
> sfunc = array_agg_transfn_strict, finalfunc = array_agg_finalfn);
> CREATE AGGREGATE
> regression=# create or replace function array_agg_transfn_strict(internal, anyelement) returns internal as
'array_agg_transfn'language internal strict immutable; 
> CREATE FUNCTION
>

nice dark trick :) -  but it doesn't work

ERROR:  aggregate 16395 needs to have compatible input type and transition type
postgres=#

Pavel



>                        regards, tom lane
>