Re: DELETE with JOIN syntax

On Wed, 27 Jul 2005, Brian Wong wrote:

> I am currently migrating from MySQL to PostgreSQL and I have found
> that some queries do not work. For instance,
>
> DELETE t1 FROM t1 LEFT JOIN t2 USING (column_id) WHERE t2.column_id IS NULL;
>
> works in MySQL. This works as expected even though the MySQL
> documentation does not mention the option of having a table between
> the keywords DELETE and FROM.
>
> I am trying to achieve the same affect for PostgreSQL so I tried
>
> DELETE FROM t1 LEFT JOIN t2 USING (column_id) WHERE t2.column_id IS NULL;
>
> and it did not work. Can someone explain to me exactly what is wrong
> with this syntax?

It's mostly that AFAIK SQL has no equivalent syntax.

> Is a table expression produced by the JOIN allowed for a DELETE?
> Im thinking that this would not work because the table expression is
> not a real table and it would not make sense for DELETE to accept such
> a parameter. How can I rewrite this query to achieve the same affect?

I think the where t2.column_id is null where column_id is the joining
column makes this a form of not exists, so maybe:

DELETE FROM t1 WHERE NOT EXISTS (SELECT 1 FROM t2 WHERE t2.column_id =
t1.columnid);