| Subject | Re: LEFT JOIN much faster than JOIN |
|---|---|
| Author | alexis_diel |
| Post date | 2013-08-02T15:28:24Z |
I can be wrong, but should make (JOIN) faster than (LEFT JOIN) only if the joined condition is using index of the joined table.
I think that if u don't have a index for the joined condition it need to seek in the whole table to filter.
In theory should not be difference between (JOIN) and (LEFT JOIN), if is used the same condition, the response brought the (FROM) table is the same, only filtering when the JOIN info is NULL or NOT.
sorry for the my awful english...
I think that if u don't have a index for the joined condition it need to seek in the whole table to filter.
In theory should not be difference between (JOIN) and (LEFT JOIN), if is used the same condition, the response brought the (FROM) table is the same, only filtering when the JOIN info is NULL or NOT.
sorry for the my awful english...
--- In firebird-support@yahoogroups.com, Josef Kokeš <j.kokes@...> wrote:
>
> On 2.8.2013 13:59, Alexis Diel wrote:
> >
> >
> > but LEFT JOIN is diferente of JOIN...
> > - LEFT JOIN brings all the data filtered from the FROM table, and
> > - JOIN brings only the data that have the ON condition in the JOINED table.
>
> Which should make JOIN faster than LEFT JOIN, if anything, because it
> can (potentionally) filter out some records.
>
> Josef
>