Re: proposal: schema variables

Hi

I am sending a strongly updated patch for schema variables.

I rewrote an execution of a LET statement. In the previous implementation I
hacked STMT_SELECT. Now, I introduced a new statement STMT_LET, and I
implemented a new executor node SetVariable. Now I think this
implementation is much cleaner. Implementation with own executor node
reduces necessary work on PL side - and allows the LET statement to be
prepared - what is important from a security view.

I'll try to write a second implementation based on a cleaner implementation
like utility command too. I expect so this version will be more simple, but
utility commands cannot be prepared, and probably, there should be special
support for any PL. I hope a cleaner implementation can help to move this
patch.

We can choose one variant in the next step and this variant can be
finalized.

Notes, comments?

Regards

Pavel