Обсуждение: where clauses and selects

Hello,

Is it possible to perform a select in the where clause of a statement?

I have a situation where I've got one arm tied behind my back:  I can
only have a single table in the select and from clauses, but the where
clause appears to be freed from that restriction.

Given a statement as follows:

   SELECT foo.foo_id, foo.name
   FROM foo, bar
   WHERE foo.bar_id = bar.bar_id
   AND bar.name = 'martini';

I'm looking for a way to recast it so that the select and from clauses
refer to a single table and the join referencing the second table
occurs in the where clause.  For example, something like this:

   SELECT foo.foo_id, foo.name
   FROM foo
   WHERE (SELECT * FROM foo, bar WHERE ...)
   foo.bar_id = bar.bar_id
   AND bar.name = 'martini';

I've explored the "where exists" clause, but it's not supported by the
application toolkit I'm using. AFAIK, I've only got access to where ...

Thanks in advance!
Scott

Scott Frankel <leknarf@pacbell.net> wrote:

> Is it possible to perform a select in the where clause of a statement?

> I have a situation where I've got one arm tied behind my
> back:  I can only have a single table in the select and from
> clauses, but the where  clause appears to be freed from that
> restriction.

> Given a statement as follows:

>   SELECT foo.foo_id, foo.name
>   FROM foo, bar
>   WHERE foo.bar_id = bar.bar_id
>   AND bar.name = 'martini';

> I'm looking for a way to recast it so that the select and
> from clauses refer to a single table and the join
> referencing the second table  occurs in the where clause.
> [...]

Something along the lines of:

| SELECT foo.foo_id, foo.name FROM foo WHERE foo.bar_id = (SELECT bar.bar_id FROM bar WHERE bar.name = 'martini');

should do the trick.

> I've explored the "where exists" clause, but it's not
> supported by the application toolkit I'm using. AFAIK, I've
> only got access to where ...

Dump it. Seriously. There are so many fine things you can do
with a full-fledged database - you certainly do not want to
be restricted in this regard.

Tim