collin.peters@gmail.com wrote:
> Basically if you rename a column, and then use the original name in a
> subquery, that sub-query does not complain that the column no longer exists,
> and seems to complete ok. This will cause whatever SELECT or DELETE that is
> using the sub-query to continue on its merry way and cause havoc.
It's not using the old name of the column --- it's using the name of the
OTHER column, that is, the column of the same name in the other table.
In essence, your subquery always returns true.
> -- select on value of 'bar' and orders for user 1
> -- FAIL - returns all three order lines of 'bar'
> SELECT *
> FROM order_lines
> WHERE value = 'bar'
> AND order_id IN (
> -- THIS SHOULD FAIL!! THIS COLUMN NAME DOES NOT EXIST ANYMORE
> SELECT order_id
> FROM users
> WHERE user_id = 1
> );
>
> -- same delete as above, except value of 'bar'
> DELETE
> FROM order_lines
> WHERE value = 'bar'
> AND order_id IN (
> -- THIS SHOULD FAIL!! THIS COLUMN NAME DOES NOT EXIST ANYMORE
> SELECT order_id
> FROM users
> WHERE user_id = 1
> );
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
