I'm not aware of MySQL supporting this feature. Microsoft does and calls it "common table expression" (CTE). The UNION is necessary as this the part that links the anchor query, Part1 of the UNION to the recursive query, Part2. Part2 of the UNION must reference the produced temporary table called "ReachableFrom" in your example. The Part2 query is put in an internal loop constantly inserting new rows into the CTE and then referencing them in the next loop. Once the loop no longer generates new rows the CTE stops and the final query is executed.
Ed -----Original Message----- From: news [mailto:[EMAIL PROTECTED] On Behalf Of Thufir Sent: Wednesday, February 27, 2008 12:28 AM To: mysql@lists.mysql.com Subject: recursion I'm reading "SQL for dummies" and one of the more interesting sections was on recursion. The example query was something like: WITH RECURSIVE ReachableFrom (Source, Destination) AS (SELECT Source, Destination FROM FLIGHT UNION SELECT in.Source, out.Destination FROM ReachableFrom in, FLIGHT out WHERE in.Destination = out.Source ) SELECT * FROM ReachableFrom WHERE Source = "Portland"; I'm a bit thrown by the union. Can this be simplified to: WITH RECURSIVE ReachableFrom (Source, Destination) AS (SELECT Source, Destination FROM FLIGHT ) SELECT * FROM ReachableFrom WHERE Source = "Portland"; thanks, Thufir -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
