On Wed, 22 Mar 2017 10:53:09 -0500 Jeffrey Mattox <j...@mac.com> wrote:
> Isn't it possible to get the same results of a RIGHT JOIN by using > two selects with a UNION or UNION ALL between them. Yes. By definition, an outer join is the union of the rows that meet the matching criteria and the rows that do not meet the matching criteria The outer join construct exists for convenience: the convenience of the user, who expresses the idea with fewer words, and the convenience of the implementer, whose query optimization problem is simplified by the direct expression of the desired result. An outer join says explicitly it wants all rows in the outer table. On the other hand, the query planner has to be quite sophisticated to recognize that A = (A where exists B) union (A where not exists B) --jkl _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users