But COALESCE is a special feature hard-wired into the parser. There's no free lunch --- you pay for your extensibility somewhere.
That's what I'm suggesting: hard-wiring LEAST and GREATEST into the parser. 7.5, maybe?
The question is: is it worth hard-wiring vs functions? (time passes) Doesn't seem to be in SQL92. It's in Oracle, Interbase and MySQL, though, says google.
I'd say we need to have LEAST and GREATEST at least somewhere in contrib (as functions) if not core, to make transition from other RDBMS to postgresql easier.
A brief test shows that we would incur quite a performance penalty (I compared COALESCE with coalesce_sql_function) if it isn't hardwiring.
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