Re: not using table aliases in where clause slow-down?

On Mon, 19 Feb 2001, Mark Cowlishaw wrote:

>
> I noticed that running queries that do -not- use declared table aliases in
> the 'where' clause seem to run a hell-of-a-lot slower than when aliases are
> used. Is there a valid reason for this? It started out as a typo but now I'm
> curious.

Well, sort of.  Technically the second query is invalid (you cannot use
the non-aliased name if you've aliased IIRC), but postgres assumes that
you really wanted additional from entries for the tables you are using
to make it valid, so:
> select
>         rel.release_id as rel_id,     rel.code as rel_code,
>         subs.subsystem_id as subs_id, subs.code as subs_code,
>         func.function_id as func_id,  func.code as func_code,
>         purp.purpose_id as purp_id,   purp.code as purp_code,
>         purp.title as purp_title,
>         proc.procedure_id as proc_id, proc.code as proc_code,
>         proc.title as proc_title
>     from
>         releases as rel, subsystems as subs,
>         functions as func, purposes as purp, procedures as proc
>     where
>         releases.project_id        = 53
>         and purposes.release_id   = releases.release_id
>         and purposes.function_id  = functions.function_id
>         and functions.subsystem_id = subsystems.subsystem_id
>         and purposes.purpose_id   = procedures.purpose_id
>     order by
>         rel.code, subs.code, func.code,
>         purp.code, proc.code;

is really:

select
         rel.release_id as rel_id,     rel.code as rel_code,
         subs.subsystem_id as subs_id, subs.code as subs_code,
         func.function_id as func_id,  func.code as func_code,
         purp.purpose_id as purp_id,   purp.code as purp_code,
         purp.title as purp_title,
         proc.procedure_id as proc_id, proc.code as proc_code,
         proc.title as proc_title
     from
         releases as rel, subsystems as subs,
         functions as func, purposes as purp, procedures as proc,
***
     releases, functions, subsystems, purposes, procedures
***
     where
         releases.project_id        = 53
         and purposes.release_id   = releases.release_id
         and purposes.function_id  = functions.function_id
         and functions.subsystem_id = subsystems.subsystem_id
         and purposes.purpose_id   = procedures.purpose_id
     order by
         rel.code, subs.code, func.code,
         purp.code, proc.code;

which is a much different query