PostgreSQL 10 Administration Cookbook - Fourth Edition

See also

• PostgreSQL 9.5 introduced the TABLESAMPLE clause into SQL. This allows you to run commands much faster by using a sample of a table's rows, giving an approximate answer. In certain cases, this can be just as useful as the most accurate answer:

postgres=# SELECT avg(id) FROM events;          avg          ---------------------  500000.500 (1 row) postgres=# SELECT  avg(id)  FROM events TABLESAMPLE system(1);          avg          ---------------------  507434.635 (1 row) postgres=# EXPLAIN (ANALYZE, BUFFERS) SELECT avg(id) FROM events;                                                        QUERY PLAN                                                        ------------------------------------------------------------------------------------------------------------------------  Aggregate (cost=16925.00..16925.01 rows=1 width=32) (actual time=204.841..204.841 rows=1 loops=1)  ...