On Wed, 19 Mar 2008, "Nikolay Samokhvalov" <[EMAIL PROTECTED]> writes: > I wonder, if the following is correct and provides expected result: > > test=# select generate_series(1, 2), generate_series(1, 4); > generate_series | generate_series > -----------------+----------------- > 1 | 1 > 2 | 2 > 1 | 3 > 2 | 4 > (4 rows) > > > 1. Is it correct at all to use SRF in select list, w/o explicit FROM? > Why then we do not allow using subselects that return multiple rows? > I'd rather expect that these two things work in similar manner. > 2. Why the query above provides 4 rows, not 2*4=8? Actually, that's > interesting -- I can use this query to find l.c.m. But it's defenetely > not that I'd expect before my try...
>From PL/scheme sources: /* * There're 2 ways to return from an SRF: * * 1. Value-per-call Mode * You return each tuple one by one via SRF_RETURN_NEXT() macro. But * PG_RETURN_DATUM() calls in the macro, makes it quite * impracticble. OTOH, this method gives opportunity to call SRFs in * a fashion like "SELECT mysrf();" * * 2. Materialize Mode * In this mode, you collect all tuples in a single set and return * that set. When compared to previos method, it's not possible to * use SRF of materialize mode like "SELECT my_materialized_srf();", * instead, you need to access it as a simple table: "SELECT * FROM * my_materialized_srf();". * * ... */ And I conclude to that generate_series() is written as a SRF function of value-per-call mode. (Also you may want to check Returning Sets[1] chapter at PostgreSQL manual.) [1] http://www.postgresql.org/docs/current/static/xfunc-c.html#XFUNC-C-RETURN-SET Regards. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
