Rule system

It's time,

    there  are  a  few small things and one big left in PL/pgSQL.
    The small things are two new statements (easy)  and  the  big
    one is to be able to return tuples and sets.

    I  decided  to  implement  the  statements  now and leave the
    tuples for later (cause they  require  changes  in  the  main
    executor).

    So next on my TODO will be the rule system.

    But  before  starting  on it I want to have a clear view onto
    the target. What is the minimum  of  capabilities,  the  rule
    system must have at least?

    Here's a start of the list:

        Retrieve-instead-retrieve  rules  on  the relation level.
        This is what builds a view (and works already - but order
        by and distinct would be nice).

        All  other  instead rules (insert, update, delete) on the
        relation level, so views  can  behave  like  real  tables
        (yeah - these can be tricky).

    What  else  must be there? I think everything on the instance
    level  is  better  done  by   triggers.   And   if   we   add
    row-/statement-level  triggers  on  SELECT, there would be no
    reason left to have  non-instead  rules.   Or  am  I  missing
    something?


Jan

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