--- Beispiel für eine Stored Procedure in Tcl

CREATE FUNCTION isSystemUser(text) RETURNS boolean
AS '
set userId $1
set retval false

set fd [open /etc/passwd r]
while {[gets $fd line] >=0} {
     set testId [lindex [split $line : ] 0]
     if {[string equal $testId $userId]} {
        set retval true
        break
     }
}
close $fd
return $retval'

LANGUAGE 'pltclu' ;

CREATE TABLE beispiel (
      username name CHECK (isSystemUser(username))
);