Robert James wrote > 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? WITH r (id) AS ( VALUES (1),(2),(2),(3),(3),(3) ) , s (id) AS ( VALUES (1), (2), (3), (3) ) SELECT id FROM r INTERSECT ALL SELECT id FROM s; Note that contrary to a mathematical set duplicate values are allowed in an SQL set (note "3" repeated twice in the final result - if you use the "ALL" form). Combine various incantation of WITH/CTE expressions to compile whatever final result you require. David J. -- View this message in context: http://postgresql.1045698.n5.nabble.com/Computing-count-of-intersection-of-two-queries-Relational-Algebra-SQL-tp5762935p5762936.html Sent from the PostgreSQL - general mailing list archive at Nabble.com. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
