On 9 April 2015 at 04:12, Michael Paquier <michael.paqu...@gmail.com> wrote:
> Also, I am wondering if the sampling logic based on block analysis is > actually correct, for example for now this fails and I think that we > should support it: > =# with query_select as (select generate_series(1, 10) as a) select > query_select.a from query_select tablesample system (100.0/11) > REPEATABLE (9999); > ERROR: 42P01: relation "query_select" does not exist > > How does the SQL spec define exactly TABLESAMPLE? Shouldn't we get a > sample from a result set? > Thoughts? Good catch. The above query doesn't make any sense. TABLESAMPLE SYSTEM implies system-defined sampling mechanism, which is block level sampling. So any block level sampling method should be barred from operating on a result set in this way... i.e. should generate an "ERROR inappropriate sampling method specified" TABLESAMPLE BERNOULLI could work in this case, or any other non-block based sampling mechanism. Whether it does work yet is another matter. This query should be part of the test suite and should generate a useful message or work correctly. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, RemoteDBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
