Roman,

R> There is no flag in RDB$PROCEDURES system table telling whether
R> procedure is selectable or not. Connectivity dirvers that are required
R> to translate abstract procedure call syntax (for example {call ...}
R> syntax in JDBC) cannot automatically generate appropriate SQL.

FWIW you could look for output parameters in the SP declaration and
use the "select" form if you find any. That's what FlameRobin does.

R> I see the need to unifying the way stored procedures are handled.

That wouldn't hurt, but it should be made in a way that's consistent
with the current syntax and semantics.

R> a) provide a new SQL statement, for example CALL, that when applied to
R> selectable procedures, returns complete result set (is equivalent to
R> SELECT * FROM), when applied to non-selectable procedures returns a
R> result set with single row corresponding to the RETURNS declaration.

I don't think an additional verb is needed. Better "fix" execute
procedure or select IMHO.

R> b) Fix the PSQL compiler to add SUSPEND before exiting the
R> non-selectable procedure if SUSPEND is not already contained in the
R> procedure body (in other words, automatically convert non-selectable
R> procedure into selectable). This allows using SELECT * FROM syntax for
R> all types of procedures.

That makes sense, also in Martijn's variation.

Ciao
--
Nando Dessena
http://www.flamerobin.org