Add support for AllTableColumns in PrimaryExpression

[tomershay]

PostgreSQL supports expressions such as posts.* (all columns from the posts table) in many places, such as the GROUP BY clause.

For example, in this query:

select c.post_id, p.* from posts p inner join comments c on c.post_id = p.post_id group by p.post_id, c.post_id, p.*;

This PR adds support for AllTableColumns in PrimaryExpression.

I wasn't sure if PrimaryExpression is the best fit for this, so will be happy for suggestions on relocating it if there's a better expression group for it.

[manticore-projects]

@tomershay

Thank you for this contribution. My understanding is: A PrimaryExpression can be used anywhere and everywhere -- which is not the case for AllColumns or AllTableColumns and especially seems to depend on the RDBMS also. However, from a pragmatical view it comes close and indeed seem to make sense.

However, we segregate both Expression at other places already and I believe even have to use semantic lookaheads (which are expensive). So in my opinion, we either

a) keep segregating AllColumns or AllTableColumns wherever it is allowed (cleaner and faster) or
b) remove all those segregations in all productions and incorporate AllColumns or AllTableColumns into PrimaryExpression (slower, but more pragmatic)

What I will not want is a mix of both approaches because it can make the Grammar even harder to maintain in the future.

[tomershay]

@manticore-projects, thanks, makes total sense.

remove all those segregations in all productions and incorporate AllColumns or AllTableColumns into PrimaryExpression (slower, but more pragmatic)

I went with the approach above, so I removed the segregation of AllColumns or AllTableColumns in other places, and added them just to PrimaryExpression.

Looking forward to hearing your thoughts.