Computing count of intersection of two queries (Relational Algebra --> SQL)

From: Robert James <srobertjames(at)gmail(dot)com>
To: Postgres General <pgsql-general(at)postgresql(dot)org>
Subject: Computing count of intersection of two queries (Relational Algebra --> SQL)
Date: 2013-07-08 01:09:42
Message-ID: CAGYyBgiquOZpPh0_aP6tOZZNAu56_gBFq4mZWRMGkj_GRWnvTQ@mail.gmail.com
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In relational algebra, I have relation R and relation S, and want to
find the cardinality of R, of S, and of R-intersect-S.

I know the SQL for R and S. What's the best way to compute the
cardinality of each relation (query) and of their intersection?

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