Обсуждение: Join Question

Question,

What is the difference between left join, and left outer join?

I know the difference between inner and outer joins, but I was thinking that left join == inner join.  But from what I am now seeing, it appears that PG is equating left join to left outer join.  Is this correct?

Thanks,

Chris

On Wed, 2006-08-02 at 14:32, Chris Hoover wrote:
> Question,
>
> What is the difference between left join, and left outer join?
>
> I know the difference between inner and outer joins, but I was
> thinking that left join == inner join.  But from what I am now seeing,
> it appears that PG is equating left join to left outer join.  Is this
> correct?

A left or right join IS an outer join, as is a full join.

the outer is just syntactic sugar.

On 8/2/06, Chris Hoover <revoohc@gmail.com> wrote:
> Question,
>
> What is the difference between left join, and left outer join?
>
> I know the difference between inner and outer joins, but I was thinking that
> left join == inner join.  But from what I am now seeing, it appears that PG
> is equating left join to left outer join.  Is this correct?

Types of JOIN:

    * [ INNER ] JOIN
    * LEFT [ OUTER ] JOIN
    * RIGHT [ OUTER ] JOIN
    * FULL [ OUTER ] JOIN
    * CROSS JOIN

As usual, "[ .. ]" means that that word can be omitted.
"left join == inner join" is absolutely incorrect, I'm afraid you need
to refresh you memory and read the manual
(http://www.postgresql.org/docs/8.1/interactive/sql-select.html, find
"join_type").

This part of Postgres conforms to standard, all major DBMSs follow
this semantics too.


--
Best regards,
Nikolay