On Wed, 13 Feb 2019, Andrew Gierth wrote:
Adrian> Close to your last posted query. person_id 2 and 3 have NULL Adrian> values for activities data as there is no record for 2 and 3 is Adrian> out of the date range.:
DISTINCT ON with no matching ORDER BY at the _same_ query level is non-deterministic. Also DISTINCT ON isn't efficient. Consider instead something along the lines of:
Andrew/Adrian, I again read about DISTINCT and DISTINCT ON and fully understand them. I've also again read about JOINs; I understand them in terms of sets and _think_ that in this query the people table is the LEFT (many) while the organizations and activities tables are the RIGHT (one) in the many-to-one relationships. That is, for each person_id there is only one org_id and only one next_contact that meets the three constraints. I'm now working on understanding how the syntax in the examples you two, Ken, and others have provided expresses the many-to-one relationships of organization and activities to people. I have the syntax that returns the next_date meeting the WHERE constraints to each person_id and am now focusing on adding the additional people and organization columns to the results. Might not be until tomorrow or Friday but I'll let you and the list subscribes know when I have understood all your suggestions and get the results I want from the query. Thanks again, Rich
