As implemented in HEAD, LATERAL means to run a nestloop in which the lateral-referencing query is run once per row of the referenced table, and the resulting rows are joined to just that row of the referenced table. So for example:
# select * from (values (2),(4)) v(x), lateral generate_series(1,x); x | generate_series ---+----------------- 2 | 1 2 | 2 4 | 1 4 | 2 4 | 3 4 | 4 (6 rows) It suddenly struck me though that there's another plausible interpretation of this syntax: perhaps we should generate all the rows of the referencing query as above, and then join them to *all* rows of the rest of the query. That is, should the above query generate x | generate_series ---+----------------- 2 | 1 2 | 1 2 | 2 2 | 2 2 | 3 2 | 4 4 | 1 4 | 1 4 | 2 4 | 2 4 | 3 4 | 4 (12 rows) This behavior doesn't seem as useful to me --- I think you'd nearly always end up adding additional WHERE clauses to get rid of the extra rows. However, there should not be any judgment calls involved here; this is a spec-defined syntax so surely the SQL standard ought to tell us what to do. But I'm darned if I see anything in the standard that defines the actual *behavior* of a LATERAL query. Please point out chapter and verse of what I'm missing. Or, perhaps we can hold some committee members' feet to the fire for a ruling? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers