Re: BUG #5001: can not prepare for where $1 is null

Hello

2009/8/21  <94487509@qq.com>:
>
> The following bug has been logged online:
>
> Bug reference: =C2=A0 =C2=A0 =C2=A05001
> Logged by:
> Email address: =C2=A0 =C2=A0 =C2=A094487509@qq.com
> PostgreSQL version: 8.3.3
> Operating system: =C2=A0 linux
> Description: =C2=A0 =C2=A0 =C2=A0 =C2=A0can not prepare for where $1 is n=
ull
> Details:
>
> why can not prepare like this? thanks!
> =C2=A0prepare ssss as select * from test where $1 is null;
> =C2=A0ERROR: =C2=A0could not determine data type of parameter $1

Probably you are thinking, so first parameter is name of column. But
this is wrong idea. You cannot parametrize column or table names. In
this case - first parameter will be constant expression - with null
value it returns all rows, with not null value - it returns no row.

If you wont to do filter query via some name you have to use dynamic sql:

create or replace function ssss(_name varchar)
returns setof test as $$
declare _r record;
begin
  for _r in execute 'select * from test where ' || quote_ident(_name)
|| ' is null'
  loop
    return next r;
  end loop;
  return;
end;
$$ language plpgsql;

regards
Pavel Stehule



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