Ladislav Lenart wrote
> * Should I alias one of the references to deal?
> * The above query works the same both with and without an alias, so is it
> simply
> a matter of taste / good practice?
> * Where can I find more info about this, i.e. when the alias is mandatory
> and
> when it is only a convenience? I've scanned through
>
>
> http://www.postgresql.org/docs/9.1/static/queries-table-expressions.html
>
> but it only mentions that subselect in FROM must have an alias. I would
> like to
> know about IN (...) and EXISTS (...).
Aliases are mandatory for self-joins. Basically two relations at the same
query level cannot have the same name. With sub-selects the inner level
shields the outer level from being visible so an alias is optional. I
believe the case of a correlated sub-query requires the alias for the same
reason - otherwise you end up with a always true where clause when joining
the supposed two deal tables together.
There is no right/best way but it is always more clear to rename such that
you avoid repeating the same relation name in the query.
David J.
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