On Fri, 15 Feb 2019, Andrew Gierth wrote:
LATERAL (SELECT ...) is syntactically like (SELECT ...) in that it comes _after_ a "," in the from-clause or after a [LEFT] JOIN keyword. Don't think of LATERAL as being a type of join, think of it as qualifying the (SELECT ...) that follows.
Andrew, Thank you. Now I understand the difference.
Rich> from activities as a Rich> where a.next_contact is not null and a.next_contact <= 'today' and Rich> a.next_contact > '2018-12-31' You'd want a condition here that references the "people" table; the whole point of LATERAL is that it opens up the scope of column references in the subquery to include those tables which are to its left in the from-clause.
And here I got it backwards, thinking the subquery could reference the columns in the people table from the initial select.
Rich> order by person_id,next_contact); and I'm guessing you want that ordered by next_contact alone, possibly with LIMIT 1 to get just the nearest following next_contact time.
That's true. With 'discrete on' only the most recent next_contact date is returned. More work over the weekend on this now I have a better understanding of lateral. Thanks again, Rich
