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Commit9007d4e

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Fix psql \d's query for identifying parent triggers.
The original coding (fromc33869c) failed with "more than one rowreturned by a subquery used as an expression" if there were unrelatedtriggers of the same tgname on parent partitioned tables. (That'spossible because statement-level triggers don't get inherited.) Fixby applying LIMIT 1 after sorting the candidates by inheritance level.Also, wrap the subquery in a CASE so that we don't have to execute it atall when the trigger is visibly non-inherited. Aside from saving somecycles, this avoids the need for a confusing and undocumented NULLIF().While here, tweak the format of the emitted query to look a bitnicer for "psql -E", and add some explanation of this subquery,because it badly needs it.Report and patch by Justin Pryzby (with some editing by me).Back-patch to v13 where the faulty code came in.Discussion:https://postgr.es/m/20211217154356.GJ17618@telsasoft.com
1 parent839f963 commit9007d4e

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‎src/bin/psql/describe.c

Lines changed: 30 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -2990,16 +2990,38 @@ describeOneTableDetails(const char *schemaname,
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printfPQExpBuffer(&buf,
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"SELECT t.tgname, "
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"pg_catalog.pg_get_triggerdef(t.oid, true), "
2993-
"t.tgenabled, t.tgisinternal, %s\n"
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"t.tgenabled, t.tgisinternal,\n");
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/*
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* Detect whether each trigger is inherited, and if so, get the name
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* of the topmost table it's inherited from. We have no easy way to
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* do that pre-v13, for lack of the tgparentid column. Even with
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* tgparentid, a straightforward search for the topmost parent would
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* require a recursive CTE, which seems unduly expensive. We cheat a
3001+
* bit by assuming parent triggers will match by tgname; then, joining
3002+
* with pg_partition_ancestors() allows the planner to make use of
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* pg_trigger_tgrelid_tgname_index if it wishes. We ensure we find
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* the correct topmost parent by stopping at the first-in-partition-
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* ancestry-order trigger that has tgparentid = 0. (There might be
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* unrelated, non-inherited triggers with the same name further up the
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* stack, so this is important.)
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*/
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if (pset.sversion >=130000)
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appendPQExpBufferStr(&buf,
3011+
" CASE WHEN t.tgparentid != 0 THEN\n"
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" (SELECT u.tgrelid::pg_catalog.regclass\n"
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" FROM pg_catalog.pg_trigger AS u,\n"
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" pg_catalog.pg_partition_ancestors(t.tgrelid) WITH ORDINALITY AS a(relid, depth)\n"
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" WHERE u.tgname = t.tgname AND u.tgrelid = a.relid\n"
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" AND u.tgparentid = 0\n"
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" ORDER BY a.depth LIMIT 1)\n"
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" END AS parent\n");
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else
3020+
appendPQExpBufferStr(&buf," NULL AS parent\n");
3021+
3022+
appendPQExpBuffer(&buf,
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"FROM pg_catalog.pg_trigger t\n"
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"WHERE t.tgrelid = '%s' AND ",
2996-
(pset.sversion >=130000 ?
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"(SELECT (NULLIF(a.relid, t.tgrelid))::pg_catalog.regclass"
2998-
" FROM pg_catalog.pg_trigger AS u, "
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" pg_catalog.pg_partition_ancestors(t.tgrelid) AS a"
3000-
" WHERE u.tgname = t.tgname AND u.tgrelid = a.relid"
3001-
" AND u.tgparentid = 0) AS parent" :
3002-
"NULL AS parent"),
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oid);
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/*

‎src/test/regress/expected/triggers.out

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2122,6 +2122,20 @@ Triggers:
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alter table trigpart attach partition trigpart3 FOR VALUES FROM (2000) to (3000); -- fail
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ERROR: trigger "trg1" for relation "trigpart3" already exists
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drop table trigpart3;
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-- check display of unrelated triggers
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create trigger samename after delete on trigpart execute function trigger_nothing();
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create trigger samename after delete on trigpart1 execute function trigger_nothing();
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\d trigpart1
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Table "public.trigpart1"
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Column | Type | Collation | Nullable | Default
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--------+---------+-----------+----------+---------
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a | integer | | |
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b | integer | | |
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Partition of: trigpart FOR VALUES FROM (0) TO (1000)
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Triggers:
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samename AFTER DELETE ON trigpart1 FOR EACH STATEMENT EXECUTE FUNCTION trigger_nothing()
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trg1 AFTER INSERT ON trigpart1 FOR EACH ROW EXECUTE FUNCTION trigger_nothing(), ON TABLE trigpart
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drop table trigpart;
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drop function trigger_nothing();
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--

‎src/test/regress/sql/triggers.sql

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1428,6 +1428,11 @@ create trigger trg1 after insert on trigpart3 for each row execute procedure tri
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altertable trigpart attach partition trigpart3 FORVALUESFROM (2000) to (3000);-- fail
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droptable trigpart3;
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-- check display of unrelated triggers
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createtriggersamename afterdeleteon trigpart execute function trigger_nothing();
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createtriggersamename afterdeleteon trigpart1 execute function trigger_nothing();
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\d trigpart1
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droptable trigpart;
14321437
dropfunction trigger_nothing();
14331438

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