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CREATE EXTENSION tsm_system_time;
CREATE TABLE test_tablesample (id int, name text);
INSERT INTO test_tablesample SELECT i, repeat(i::text, 1000)
FROM generate_series(0, 30) s(i);
ANALYZE test_tablesample;
-- It's a bit tricky to test SYSTEM_TIME in a platform-independent way.
-- We can test the zero-time corner case ...
SELECT count(*) FROM test_tablesample TABLESAMPLE system_time (0);
count
-------
0
(1 row)
-- ... and we assume that this will finish before running out of time:
SELECT count(*) FROM test_tablesample TABLESAMPLE system_time (100000);
count
-------
31
(1 row)
-- bad parameters should get through planning, but not execution:
EXPLAIN (COSTS OFF)
SELECT id FROM test_tablesample TABLESAMPLE system_time (-1);
QUERY PLAN
--------------------------------------------------
Sample Scan on test_tablesample
Sampling: system_time ('-1'::double precision)
(2 rows)
SELECT id FROM test_tablesample TABLESAMPLE system_time (-1);
ERROR: sample collection time must not be negative
-- fail, this method is not repeatable:
SELECT * FROM test_tablesample TABLESAMPLE system_time (10) REPEATABLE (0);
ERROR: tablesample method system_time does not support REPEATABLE
LINE 1: SELECT * FROM test_tablesample TABLESAMPLE system_time (10) ...
^
-- since it's not repeatable, we expect a Materialize node in these plans:
EXPLAIN (COSTS OFF)
SELECT * FROM
(VALUES (0),(100000)) v(time),
LATERAL (SELECT COUNT(*) FROM test_tablesample
TABLESAMPLE system_time (100000)) ss;
QUERY PLAN
------------------------------------------------------------------------
Nested Loop
-> Aggregate
-> Materialize
-> Sample Scan on test_tablesample
Sampling: system_time ('100000'::double precision)
-> Values Scan on "*VALUES*"
(6 rows)
SELECT * FROM
(VALUES (0),(100000)) v(time),
LATERAL (SELECT COUNT(*) FROM test_tablesample
TABLESAMPLE system_time (100000)) ss;
time | count
--------+-------
0 | 31
100000 | 31
(2 rows)
EXPLAIN (COSTS OFF)
SELECT * FROM
(VALUES (0),(100000)) v(time),
LATERAL (SELECT COUNT(*) FROM test_tablesample
TABLESAMPLE system_time (time)) ss;
QUERY PLAN
----------------------------------------------------------------
Nested Loop
-> Values Scan on "*VALUES*"
-> Aggregate
-> Materialize
-> Sample Scan on test_tablesample
Sampling: system_time ("*VALUES*".column1)
(6 rows)
SELECT * FROM
(VALUES (0),(100000)) v(time),
LATERAL (SELECT COUNT(*) FROM test_tablesample
TABLESAMPLE system_time (time)) ss;
time | count
--------+-------
0 | 0
100000 | 31
(2 rows)
CREATE VIEW vv AS
SELECT * FROM test_tablesample TABLESAMPLE system_time (20);
EXPLAIN (COSTS OFF) SELECT * FROM vv;
QUERY PLAN
--------------------------------------------------
Sample Scan on test_tablesample
Sampling: system_time ('20'::double precision)
(2 rows)
DROP EXTENSION tsm_system_time; -- fail, view depends on extension
ERROR: cannot drop extension tsm_system_time because other objects depend on it
DETAIL: view vv depends on function system_time(internal)
HINT: Use DROP ... CASCADE to drop the dependent objects too.
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