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c6bc655ee2
Both bugs #16676[1] and #17141[2] illustrate that the combination of SKIP LOCKED and FETCH FIRST WITH TIES break expectations when it comes to rows returned to other sessions accessing the same row. Since this situation is detectable from the syntax and hard to fix otherwise, forbid for now, with the potential to fix in the future. [1] https://postgr.es/m/16676-fd62c3c835880da6@postgresql.org [2] https://postgr.es/m/17141-913d78b9675aac8e@postgresql.org Backpatch-through: 13, where WITH TIES was introduced Author: David Christensen <david.christensen@crunchydata.com> Discussion: https://postgr.es/m/CAOxo6XLPccCKru3xPMaYDpa+AXyPeWFs+SskrrL+HKwDjJnLhg@mail.gmail.com
201 lines
5.9 KiB
PL/PgSQL
201 lines
5.9 KiB
PL/PgSQL
--
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-- LIMIT
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-- Check the LIMIT/OFFSET feature of SELECT
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--
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SELECT ''::text AS two, unique1, unique2, stringu1
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FROM onek WHERE unique1 > 50
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ORDER BY unique1 LIMIT 2;
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SELECT ''::text AS five, unique1, unique2, stringu1
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FROM onek WHERE unique1 > 60
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ORDER BY unique1 LIMIT 5;
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SELECT ''::text AS two, unique1, unique2, stringu1
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FROM onek WHERE unique1 > 60 AND unique1 < 63
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ORDER BY unique1 LIMIT 5;
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SELECT ''::text AS three, unique1, unique2, stringu1
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FROM onek WHERE unique1 > 100
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ORDER BY unique1 LIMIT 3 OFFSET 20;
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SELECT ''::text AS zero, unique1, unique2, stringu1
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FROM onek WHERE unique1 < 50
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ORDER BY unique1 DESC LIMIT 8 OFFSET 99;
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SELECT ''::text AS eleven, unique1, unique2, stringu1
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FROM onek WHERE unique1 < 50
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ORDER BY unique1 DESC LIMIT 20 OFFSET 39;
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SELECT ''::text AS ten, unique1, unique2, stringu1
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FROM onek
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ORDER BY unique1 OFFSET 990;
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SELECT ''::text AS five, unique1, unique2, stringu1
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FROM onek
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ORDER BY unique1 OFFSET 990 LIMIT 5;
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SELECT ''::text AS five, unique1, unique2, stringu1
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FROM onek
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ORDER BY unique1 LIMIT 5 OFFSET 900;
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-- Test null limit and offset. The planner would discard a simple null
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-- constant, so to ensure executor is exercised, do this:
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select * from int8_tbl limit (case when random() < 0.5 then null::bigint end);
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select * from int8_tbl offset (case when random() < 0.5 then null::bigint end);
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-- Test assorted cases involving backwards fetch from a LIMIT plan node
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begin;
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declare c1 cursor for select * from int8_tbl limit 10;
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fetch all in c1;
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fetch 1 in c1;
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fetch backward 1 in c1;
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fetch backward all in c1;
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fetch backward 1 in c1;
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fetch all in c1;
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declare c2 cursor for select * from int8_tbl limit 3;
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fetch all in c2;
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fetch 1 in c2;
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fetch backward 1 in c2;
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fetch backward all in c2;
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fetch backward 1 in c2;
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fetch all in c2;
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declare c3 cursor for select * from int8_tbl offset 3;
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fetch all in c3;
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fetch 1 in c3;
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fetch backward 1 in c3;
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fetch backward all in c3;
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fetch backward 1 in c3;
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fetch all in c3;
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declare c4 cursor for select * from int8_tbl offset 10;
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fetch all in c4;
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fetch 1 in c4;
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fetch backward 1 in c4;
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fetch backward all in c4;
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fetch backward 1 in c4;
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fetch all in c4;
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declare c5 cursor for select * from int8_tbl order by q1 fetch first 2 rows with ties;
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fetch all in c5;
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fetch 1 in c5;
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fetch backward 1 in c5;
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fetch backward 1 in c5;
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fetch all in c5;
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fetch backward all in c5;
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fetch all in c5;
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fetch backward all in c5;
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rollback;
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-- Stress test for variable LIMIT in conjunction with bounded-heap sorting
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SELECT
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(SELECT n
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FROM (VALUES (1)) AS x,
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(SELECT n FROM generate_series(1,10) AS n
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ORDER BY n LIMIT 1 OFFSET s-1) AS y) AS z
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FROM generate_series(1,10) AS s;
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--
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-- Test behavior of volatile and set-returning functions in conjunction
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-- with ORDER BY and LIMIT.
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--
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create temp sequence testseq;
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explain (verbose, costs off)
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select unique1, unique2, nextval('testseq')
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from tenk1 order by unique2 limit 10;
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select unique1, unique2, nextval('testseq')
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from tenk1 order by unique2 limit 10;
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select currval('testseq');
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explain (verbose, costs off)
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select unique1, unique2, nextval('testseq')
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from tenk1 order by tenthous limit 10;
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select unique1, unique2, nextval('testseq')
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from tenk1 order by tenthous limit 10;
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select currval('testseq');
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explain (verbose, costs off)
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select unique1, unique2, generate_series(1,10)
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from tenk1 order by unique2 limit 7;
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select unique1, unique2, generate_series(1,10)
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from tenk1 order by unique2 limit 7;
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explain (verbose, costs off)
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select unique1, unique2, generate_series(1,10)
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from tenk1 order by tenthous limit 7;
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select unique1, unique2, generate_series(1,10)
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from tenk1 order by tenthous limit 7;
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-- use of random() is to keep planner from folding the expressions together
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explain (verbose, costs off)
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select generate_series(0,2) as s1, generate_series((random()*.1)::int,2) as s2;
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select generate_series(0,2) as s1, generate_series((random()*.1)::int,2) as s2;
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explain (verbose, costs off)
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select generate_series(0,2) as s1, generate_series((random()*.1)::int,2) as s2
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order by s2 desc;
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select generate_series(0,2) as s1, generate_series((random()*.1)::int,2) as s2
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order by s2 desc;
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-- test for failure to set all aggregates' aggtranstype
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explain (verbose, costs off)
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select sum(tenthous) as s1, sum(tenthous) + random()*0 as s2
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from tenk1 group by thousand order by thousand limit 3;
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select sum(tenthous) as s1, sum(tenthous) + random()*0 as s2
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from tenk1 group by thousand order by thousand limit 3;
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--
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-- FETCH FIRST
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-- Check the WITH TIES clause
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--
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SELECT thousand
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FROM onek WHERE thousand < 5
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ORDER BY thousand FETCH FIRST 2 ROW WITH TIES;
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SELECT thousand
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FROM onek WHERE thousand < 5
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ORDER BY thousand FETCH FIRST ROWS WITH TIES;
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SELECT thousand
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FROM onek WHERE thousand < 5
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ORDER BY thousand FETCH FIRST 1 ROW WITH TIES;
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SELECT thousand
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FROM onek WHERE thousand < 5
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ORDER BY thousand FETCH FIRST 2 ROW ONLY;
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-- SKIP LOCKED and WITH TIES are incompatible
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SELECT thousand
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FROM onek WHERE thousand < 5
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ORDER BY thousand FETCH FIRST 1 ROW WITH TIES FOR UPDATE SKIP LOCKED;
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-- should fail
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SELECT ''::text AS two, unique1, unique2, stringu1
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FROM onek WHERE unique1 > 50
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FETCH FIRST 2 ROW WITH TIES;
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-- test ruleutils
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CREATE VIEW limit_thousand_v_1 AS SELECT thousand FROM onek WHERE thousand < 995
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ORDER BY thousand FETCH FIRST 5 ROWS WITH TIES OFFSET 10;
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\d+ limit_thousand_v_1
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CREATE VIEW limit_thousand_v_2 AS SELECT thousand FROM onek WHERE thousand < 995
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ORDER BY thousand OFFSET 10 FETCH FIRST 5 ROWS ONLY;
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\d+ limit_thousand_v_2
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CREATE VIEW limit_thousand_v_3 AS SELECT thousand FROM onek WHERE thousand < 995
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ORDER BY thousand FETCH FIRST NULL ROWS WITH TIES; -- fails
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CREATE VIEW limit_thousand_v_3 AS SELECT thousand FROM onek WHERE thousand < 995
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ORDER BY thousand FETCH FIRST (NULL+1) ROWS WITH TIES;
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\d+ limit_thousand_v_3
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CREATE VIEW limit_thousand_v_4 AS SELECT thousand FROM onek WHERE thousand < 995
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ORDER BY thousand FETCH FIRST NULL ROWS ONLY;
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\d+ limit_thousand_v_4
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-- leave these views
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