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6ef77cf46e
This patch causes EXPLAIN to always assign a separate table alias to the parent RTE of an append relation (inheritance set); before, such RTEs were ignored if not actually scanned by the plan. Since the child RTEs now always have that same alias to start with (cf. commit55a1954da), the net effect is that the parent RTE usually gets the alias used or implied by the query text, and the children all get that alias with "_N" appended. (The exception to "usually" is if there are duplicate aliases in different subtrees of the original query; then some of those original RTEs will also have "_N" appended.) This results in more uniform output for partitioned-table plans than we had before: the partitioned table itself gets the original alias, and all child tables have aliases with "_N", rather than the previous behavior where one of the children would get an alias without "_N". The reason for giving the parent RTE an alias, even if it isn't scanned by the plan, is that we now use the parent's alias to qualify Vars that refer to an appendrel output column and appear above the Append or MergeAppend that computes the appendrel. But below the append, Vars refer to some one of the child relations, and are displayed that way. This seems clearer than the old behavior where a Var that could carry values from any child relation was displayed as if it referred to only one of them. While at it, change ruleutils.c so that the code paths used by EXPLAIN deal in Plan trees not PlanState trees. This effectively reverts a decision made in commit1cc29fe7c, which seemed like a good idea at the time to make ruleutils.c consistent with explain.c. However, it's problematic because we'd really like to allow executor startup pruning to remove all the children of an append node when possible, leaving no child PlanState to resolve Vars against. (That's not done here, but will be in the next patch.) This requires different handling of subplans and initplans than before, but is otherwise a pretty straightforward change. Discussion: https://postgr.es/m/001001d4f44b$2a2cca50$7e865ef0$@lab.ntt.co.jp
332 lines
8.6 KiB
Plaintext
332 lines
8.6 KiB
Plaintext
CREATE TABLE test_tablesample (id int, name text) WITH (fillfactor=10);
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-- use fillfactor so we don't have to load too much data to get multiple pages
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INSERT INTO test_tablesample
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SELECT i, repeat(i::text, 200) FROM generate_series(0, 9) s(i);
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SELECT t.id FROM test_tablesample AS t TABLESAMPLE SYSTEM (50) REPEATABLE (0);
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id
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----
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3
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4
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5
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6
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7
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8
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(6 rows)
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (100.0/11) REPEATABLE (0);
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id
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----
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(0 rows)
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (50) REPEATABLE (0);
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id
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----
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3
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4
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5
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6
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7
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8
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(6 rows)
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SELECT id FROM test_tablesample TABLESAMPLE BERNOULLI (50) REPEATABLE (0);
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id
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----
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4
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5
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6
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7
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8
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(5 rows)
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SELECT id FROM test_tablesample TABLESAMPLE BERNOULLI (5.5) REPEATABLE (0);
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id
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----
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7
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(1 row)
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-- 100% should give repeatable count results (ie, all rows) in any case
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SELECT count(*) FROM test_tablesample TABLESAMPLE SYSTEM (100);
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count
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-------
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10
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(1 row)
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SELECT count(*) FROM test_tablesample TABLESAMPLE SYSTEM (100) REPEATABLE (1+2);
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count
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-------
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10
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(1 row)
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SELECT count(*) FROM test_tablesample TABLESAMPLE SYSTEM (100) REPEATABLE (0.4);
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count
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-------
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10
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(1 row)
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CREATE VIEW test_tablesample_v1 AS
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (10*2) REPEATABLE (2);
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CREATE VIEW test_tablesample_v2 AS
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (99);
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\d+ test_tablesample_v1
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View "public.test_tablesample_v1"
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Column | Type | Collation | Nullable | Default | Storage | Description
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--------+---------+-----------+----------+---------+---------+-------------
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id | integer | | | | plain |
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View definition:
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SELECT test_tablesample.id
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FROM test_tablesample TABLESAMPLE system ((10 * 2)) REPEATABLE (2);
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\d+ test_tablesample_v2
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View "public.test_tablesample_v2"
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Column | Type | Collation | Nullable | Default | Storage | Description
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--------+---------+-----------+----------+---------+---------+-------------
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id | integer | | | | plain |
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View definition:
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SELECT test_tablesample.id
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FROM test_tablesample TABLESAMPLE system (99);
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-- check a sampled query doesn't affect cursor in progress
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BEGIN;
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DECLARE tablesample_cur CURSOR FOR
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (50) REPEATABLE (0);
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FETCH FIRST FROM tablesample_cur;
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id
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----
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3
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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4
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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5
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(1 row)
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (50) REPEATABLE (0);
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id
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----
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3
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4
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5
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6
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7
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8
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(6 rows)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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6
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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7
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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8
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(1 row)
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FETCH FIRST FROM tablesample_cur;
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id
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----
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3
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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4
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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5
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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6
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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7
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(1 row)
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FETCH NEXT FROM tablesample_cur;
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id
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----
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8
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(1 row)
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CLOSE tablesample_cur;
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END;
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EXPLAIN (COSTS OFF)
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (50) REPEATABLE (2);
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QUERY PLAN
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--------------------------------------------------------------------
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Sample Scan on test_tablesample
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Sampling: system ('50'::real) REPEATABLE ('2'::double precision)
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(2 rows)
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EXPLAIN (COSTS OFF)
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SELECT * FROM test_tablesample_v1;
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QUERY PLAN
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--------------------------------------------------------------------
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Sample Scan on test_tablesample
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Sampling: system ('20'::real) REPEATABLE ('2'::double precision)
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(2 rows)
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-- check inheritance behavior
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explain (costs off)
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select count(*) from person tablesample bernoulli (100);
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QUERY PLAN
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-------------------------------------------------
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Aggregate
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-> Append
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-> Sample Scan on person person_1
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Sampling: bernoulli ('100'::real)
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-> Sample Scan on emp person_2
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Sampling: bernoulli ('100'::real)
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-> Sample Scan on student person_3
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Sampling: bernoulli ('100'::real)
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-> Sample Scan on stud_emp person_4
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Sampling: bernoulli ('100'::real)
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(10 rows)
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select count(*) from person tablesample bernoulli (100);
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count
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-------
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58
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(1 row)
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select count(*) from person;
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count
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-------
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58
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(1 row)
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-- check that collations get assigned within the tablesample arguments
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SELECT count(*) FROM test_tablesample TABLESAMPLE bernoulli (('1'::text < '0'::text)::int);
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count
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-------
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0
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(1 row)
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-- check behavior during rescans, as well as correct handling of min/max pct
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select * from
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(values (0),(100)) v(pct),
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lateral (select count(*) from tenk1 tablesample bernoulli (pct)) ss;
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pct | count
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-----+-------
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0 | 0
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100 | 10000
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(2 rows)
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select * from
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(values (0),(100)) v(pct),
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lateral (select count(*) from tenk1 tablesample system (pct)) ss;
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pct | count
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-----+-------
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0 | 0
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100 | 10000
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(2 rows)
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explain (costs off)
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select pct, count(unique1) from
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(values (0),(100)) v(pct),
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lateral (select * from tenk1 tablesample bernoulli (pct)) ss
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group by pct;
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QUERY PLAN
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--------------------------------------------------------
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HashAggregate
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Group Key: "*VALUES*".column1
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-> Nested Loop
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-> Values Scan on "*VALUES*"
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-> Sample Scan on tenk1
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Sampling: bernoulli ("*VALUES*".column1)
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(6 rows)
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select pct, count(unique1) from
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(values (0),(100)) v(pct),
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lateral (select * from tenk1 tablesample bernoulli (pct)) ss
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group by pct;
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pct | count
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-----+-------
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100 | 10000
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(1 row)
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select pct, count(unique1) from
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(values (0),(100)) v(pct),
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lateral (select * from tenk1 tablesample system (pct)) ss
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group by pct;
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pct | count
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-----+-------
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100 | 10000
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(1 row)
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-- errors
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SELECT id FROM test_tablesample TABLESAMPLE FOOBAR (1);
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ERROR: tablesample method foobar does not exist
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LINE 1: SELECT id FROM test_tablesample TABLESAMPLE FOOBAR (1);
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^
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (NULL);
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ERROR: TABLESAMPLE parameter cannot be null
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (50) REPEATABLE (NULL);
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ERROR: TABLESAMPLE REPEATABLE parameter cannot be null
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SELECT id FROM test_tablesample TABLESAMPLE BERNOULLI (-1);
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ERROR: sample percentage must be between 0 and 100
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SELECT id FROM test_tablesample TABLESAMPLE BERNOULLI (200);
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ERROR: sample percentage must be between 0 and 100
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (-1);
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ERROR: sample percentage must be between 0 and 100
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SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (200);
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ERROR: sample percentage must be between 0 and 100
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SELECT id FROM test_tablesample_v1 TABLESAMPLE BERNOULLI (1);
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ERROR: TABLESAMPLE clause can only be applied to tables and materialized views
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LINE 1: SELECT id FROM test_tablesample_v1 TABLESAMPLE BERNOULLI (1)...
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^
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INSERT INTO test_tablesample_v1 VALUES(1);
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ERROR: cannot insert into view "test_tablesample_v1"
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DETAIL: Views containing TABLESAMPLE are not automatically updatable.
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HINT: To enable inserting into the view, provide an INSTEAD OF INSERT trigger or an unconditional ON INSERT DO INSTEAD rule.
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WITH query_select AS (SELECT * FROM test_tablesample)
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SELECT * FROM query_select TABLESAMPLE BERNOULLI (5.5) REPEATABLE (1);
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ERROR: TABLESAMPLE clause can only be applied to tables and materialized views
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LINE 2: SELECT * FROM query_select TABLESAMPLE BERNOULLI (5.5) REPEA...
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^
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SELECT q.* FROM (SELECT * FROM test_tablesample) as q TABLESAMPLE BERNOULLI (5);
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ERROR: syntax error at or near "TABLESAMPLE"
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LINE 1: ...CT q.* FROM (SELECT * FROM test_tablesample) as q TABLESAMPL...
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^
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-- check partitioned tables support tablesample
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create table parted_sample (a int) partition by list (a);
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create table parted_sample_1 partition of parted_sample for values in (1);
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create table parted_sample_2 partition of parted_sample for values in (2);
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explain (costs off)
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select * from parted_sample tablesample bernoulli (100);
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QUERY PLAN
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-------------------------------------------
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Append
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-> Sample Scan on parted_sample_1
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Sampling: bernoulli ('100'::real)
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-> Sample Scan on parted_sample_2
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Sampling: bernoulli ('100'::real)
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(5 rows)
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drop table parted_sample, parted_sample_1, parted_sample_2;
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