Chris Spotts: Why Oracle rownum just isn't LIMIT...*sigh*

There times (not often, but times) where its really useful to write something like...

In Postgres I can do this:

SELECT

...

(SELECT some_value from table_bar bar where bar.foo_id = foo.foo_id 

    order by some_date LIMIT 1) as some_value_from_bar

FROM

table_foo foo;

However in Oracle, there's rownum, but this doesn't work:

SELECT

...

(SELECT some_value from table_bar bar where bar.foo_id = foo.foo_id 

     and rownum = 1 order by some_date) as some_value_from_bar

FROM

table_foo foo;

That doesn't work because the where clauses there is evaluated before the order by.

Can't do this either:

SELECT

...

(SELECT some_value from ( SELECT some_value from table_bar bar 

    where bar.foo_id = foo.foo_id order by some_date) t1 where rownum = 1 ) as some_value_from_bar

FROM

table_foo foo;

The inner query doesn't have the scope to pull in from table_foo anymore.

You can get around this with JOINing and filtering, but often times that subselect performance is just fine and much much more clear.
I just wish there was a real LIMIT in Oracle (or that we did our main app in Postgres).