Vlad,

V> a) value as param

V> looks not very good for me as value may have AS word inside and confuse
V> reader. Also i prefer to see param name before expression.

These are the same issues you have with aliases in select statements.
People have gotten used to them by now. :-)
BTW, for full sonsistency it should be [as] (optional).

I see that you and Adriano use "prefer" and "don't like" as arguments.
I can't counter that. :-)

V> b) param is value

V> looks better for me

Although it's a bit overloaded, since it's used as part of IS NULL and IS
DISTINCT.

V> c) param := value

V> looks almost ok

Doesn't look like SQL, though.

V> d) param <= value, or value => param

Same as above.
Ciao
--
Nando Dessena