Re: Implicit casting and JOIN syntax constraints

On Fri, Jan 17, 2003 at 06:48:28AM -0800, Roman Fail wrote:
> It seems to me that this should absolutely go on the TODO list.
> Why does the planner require an explicit cast when the implicit
> cast is so obvious? Does Oracle do this? I can assure you that
> MSSQL does not.

The reason it happens is because of the flexible datatype system in
PostgreSQL. Because it's easy to add a datatype, you pay in other
ways. The problem is coming up with a nice, clean set of rules for
coercion. See the link that Tom Lane posted, and the thousands of
other discussions around this in the archives. Yes, it's a pain.
Everyone knows that. A complete solution is what's missing.

> too. I've been writing SQL queries for 10 years in FoxPro, Access,
> SQL Server, MySQL, and Sybase. I have never come across this very
> confusing "feature" until now.

Well, there are differences between every system. Indeed, the "SQL"
of MySQL is so far from anything resembling the standard that one
could argue it doesn't comply at all. You're right that it means a
steep learning curve for some things, and the problems can be
frustrating. But that doesn't mean you want to throw the baby out
with the bathwater. The ability to give the planner hints through
the JOIN syntax is, frankly, a real help when you're faced with
certain kinds of performance problems. Some systems don't give you a
knob to tune there at all. Is it different from other systems?
Sure. Is that automatically a reason to pitch the feature? No.
(Further discussion of this probably belongs on -general, if
anywhere, by the way.)

A

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