See equijoin
predicate and
simple
column reference for definitions. For example,
transforms the
following query:
SELECT * FROM samp.employee e, samp.emp_act a, samp.emp_resume r
WHERE e.empno = a.empno
and a.empno = r.empno
into the following:
SELECT * FROM samp.employee e, samp.emp_act a, samp.emp_resume r
WHERE e.empno = a.empno
and a.empno = r.empno
and e.empno = r.empno
On the other hand, the optimizer knows that one of these equijoin predicates
is redundant and will throw out the one that is least useful for
optimization.