Re: delta relations in AFTER triggers

Marti Raudsepp <marti(at)juffo(dot)org> wrote:

> The real point I was trying to convey (in my previous email) is
> that these declarations should be part of the trigger *function*
> not the function-to-table relationship. CREATE TRIGGER shouldn't
> be in the business of declaring new local variables for the
> trigger function. Whether we define new syntax for that or re-use
> the argument list is secondary.

I think the reason the standard includes it in the trigger
definition is that it allows the trigger code to be specified in
the CREATE TRIGGER statement; and in fact, PostgreSQL is the first
database product I have used which requires a trigger function to
be created first.

<triggered action> ::=
  [ FOR EACH { ROW | STATEMENT } ]
      [ WHEN <left paren> <search condition> <right paren> ]
      <triggered SQL statement>

<triggered SQL statement> ::=
    <SQL procedure statement>
  | BEGIN ATOMIC { <SQL procedure statement> <semicolon> }... END

If we ever support this part of the standard, we need to be able to
specify these in the CREATE TRIGGER statement (or stay with the
concept of reserving "special names" for these relations).  So if
we use non-standard syntax now, we are likely to be looking at an
ugly hybrid of techniques in the future.

That said, if we want to have a way to specify this for a function
(for now), we could use the CREATE FUNCTION's WITH clause.  I
assume that a mismatch between the name specified there and the
name which is used in the function body would be a run-time error
when the trigger function is fired, not an error at the time that
CREATE FUNCTION is run, since we only ensure valid syntax at CREATE
FUNCTION time; we don't resolve any table names or column names at
that time.  For example, on a freshly-created database with no
tables created:

test=# create function xxx() returns trigger language plpgsql
test-# as $$ begin update adsf set qwerty = 'xxx'; end; $$;
CREATE FUNCTION

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company