From: Jeff Davis Date: Sun, 8 Jul 2018 07:14:51 +0000 (-0700) Subject: Fix WITH CHECK OPTION on views referencing postgres_fdw tables. X-Git-Tag: REL_12_BETA1~1917 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=a45adc747e271556eb9443973264bf3353c86524;p=postgresql Fix WITH CHECK OPTION on views referencing postgres_fdw tables. If a view references a foreign table, and the foreign table has a BEFORE INSERT trigger, then it's possible for a tuple inserted or updated through the view to be changed such that it violates the view's WITH CHECK OPTION constraint. Before this commit, postgres_fdw handled this case inconsistently. A RETURNING clause on the INSERT or UPDATE statement targeting the view would cause the finally-inserted tuple to be read back, and the WITH CHECK OPTION violation would throw an error. But without a RETURNING clause, postgres_fdw would not read the final tuple back, and WITH CHECK OPTION would not throw an error for the violation (or may throw an error when there is no real violation). AFTER ROW triggers on the foreign table had a similar effect as a RETURNING clause on the INSERT or UPDATE statement. To fix, this commit retrieves the attributes needed to enforce the WITH CHECK OPTION constraint along with the attributes needed for the RETURNING clause (if any) from the remote side. Thus, the WITH CHECK OPTION constraint is always evaluated against the final tuple after any triggers on the remote side. This fix may be considered inconsistent with CHECK constraints declared on foreign tables, which are not enforced locally at all (because the constraint is on a remote object). The discussion concluded that this difference is reasonable, because the WITH CHECK OPTION is a constraint on the local view (not any remote object); therefore it only makes sense to enforce its WITH CHECK OPTION constraint locally. Author: Etsuro Fujita Reviewed-by: Arthur Zakirov, Stephen Frost Discussion: https://www.postgresql.org/message-id/7eb58fab-fd3b-781b-ac33-f7cfec96021f%40lab.ntt.co.jp --- diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c index 8068e28184..6001f4d25e 100644 --- a/contrib/postgres_fdw/deparse.c +++ b/contrib/postgres_fdw/deparse.c @@ -140,6 +140,7 @@ static void deparseSubqueryTargetList(deparse_expr_cxt *context); static void deparseReturningList(StringInfo buf, RangeTblEntry *rte, Index rtindex, Relation rel, bool trig_after_row, + List *withCheckOptionList, List *returningList, List **retrieved_attrs); static void deparseColumnRef(StringInfo buf, int varno, int varattno, @@ -1645,14 +1646,15 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel, * deparse remote INSERT statement * * The statement text is appended to buf, and we also create an integer List - * of the columns being retrieved by RETURNING (if any), which is returned - * to *retrieved_attrs. + * of the columns being retrieved by WITH CHECK OPTION or RETURNING (if any), + * which is returned to *retrieved_attrs. */ void deparseInsertSql(StringInfo buf, RangeTblEntry *rte, Index rtindex, Relation rel, List *targetAttrs, bool doNothing, - List *returningList, List **retrieved_attrs) + List *withCheckOptionList, List *returningList, + List **retrieved_attrs) { AttrNumber pindex; bool first; @@ -1701,20 +1703,21 @@ deparseInsertSql(StringInfo buf, RangeTblEntry *rte, deparseReturningList(buf, rte, rtindex, rel, rel->trigdesc && rel->trigdesc->trig_insert_after_row, - returningList, retrieved_attrs); + withCheckOptionList, returningList, retrieved_attrs); } /* * deparse remote UPDATE statement * * The statement text is appended to buf, and we also create an integer List - * of the columns being retrieved by RETURNING (if any), which is returned - * to *retrieved_attrs. + * of the columns being retrieved by WITH CHECK OPTION or RETURNING (if any), + * which is returned to *retrieved_attrs. */ void deparseUpdateSql(StringInfo buf, RangeTblEntry *rte, Index rtindex, Relation rel, - List *targetAttrs, List *returningList, + List *targetAttrs, + List *withCheckOptionList, List *returningList, List **retrieved_attrs) { AttrNumber pindex; @@ -1743,7 +1746,7 @@ deparseUpdateSql(StringInfo buf, RangeTblEntry *rte, deparseReturningList(buf, rte, rtindex, rel, rel->trigdesc && rel->trigdesc->trig_update_after_row, - returningList, retrieved_attrs); + withCheckOptionList, returningList, retrieved_attrs); } /* @@ -1837,7 +1840,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root, &context); else deparseReturningList(buf, rte, rtindex, rel, false, - returningList, retrieved_attrs); + NIL, returningList, retrieved_attrs); } /* @@ -1859,7 +1862,7 @@ deparseDeleteSql(StringInfo buf, RangeTblEntry *rte, deparseReturningList(buf, rte, rtindex, rel, rel->trigdesc && rel->trigdesc->trig_delete_after_row, - returningList, retrieved_attrs); + NIL, returningList, retrieved_attrs); } /* @@ -1921,7 +1924,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root, else deparseReturningList(buf, planner_rt_fetch(rtindex, root), rtindex, rel, false, - returningList, retrieved_attrs); + NIL, returningList, retrieved_attrs); } /* @@ -1931,6 +1934,7 @@ static void deparseReturningList(StringInfo buf, RangeTblEntry *rte, Index rtindex, Relation rel, bool trig_after_row, + List *withCheckOptionList, List *returningList, List **retrieved_attrs) { @@ -1943,6 +1947,21 @@ deparseReturningList(StringInfo buf, RangeTblEntry *rte, bms_make_singleton(0 - FirstLowInvalidHeapAttributeNumber); } + if (withCheckOptionList != NIL) + { + /* + * We need the attrs, non-system and system, mentioned in the local + * query's WITH CHECK OPTION list. + * + * Note: we do this to ensure that WCO constraints will be evaluated + * on the data actually inserted/updated on the remote side, which + * might differ from the data supplied by the core code, for example + * as a result of remote triggers. + */ + pull_varattnos((Node *) withCheckOptionList, rtindex, + &attrs_used); + } + if (returningList != NIL) { /* diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index cf4863c5aa..8c58720df6 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -6173,10 +6173,12 @@ ALTER FOREIGN TABLE ft1 DROP CONSTRAINT ft1_c2negative; -- =================================================================== -- test WITH CHECK OPTION constraints -- =================================================================== +CREATE FUNCTION row_before_insupd_trigfunc() RETURNS trigger AS $$BEGIN NEW.a := NEW.a + 10; RETURN NEW; END$$ LANGUAGE plpgsql; CREATE TABLE base_tbl (a int, b int); ALTER TABLE base_tbl SET (autovacuum_enabled = 'false'); +CREATE TRIGGER row_before_insupd_trigger BEFORE INSERT OR UPDATE ON base_tbl FOR EACH ROW EXECUTE PROCEDURE row_before_insupd_trigfunc(); CREATE FOREIGN TABLE foreign_tbl (a int, b int) - SERVER loopback OPTIONS(table_name 'base_tbl'); + SERVER loopback OPTIONS (table_name 'base_tbl'); CREATE VIEW rw_view AS SELECT * FROM foreign_tbl WHERE a < b WITH CHECK OPTION; \d+ rw_view @@ -6192,45 +6194,162 @@ View definition: WHERE foreign_tbl.a < foreign_tbl.b; Options: check_option=cascaded -INSERT INTO rw_view VALUES (0, 10); -- ok -INSERT INTO rw_view VALUES (10, 0); -- should fail +EXPLAIN (VERBOSE, COSTS OFF) +INSERT INTO rw_view VALUES (0, 5); + QUERY PLAN +-------------------------------------------------------------------------------- + Insert on public.foreign_tbl + Remote SQL: INSERT INTO public.base_tbl(a, b) VALUES ($1, $2) RETURNING a, b + -> Result + Output: 0, 5 +(4 rows) + +INSERT INTO rw_view VALUES (0, 5); -- should fail ERROR: new row violates check option for view "rw_view" -DETAIL: Failing row contains (10, 0). +DETAIL: Failing row contains (10, 5). EXPLAIN (VERBOSE, COSTS OFF) -UPDATE rw_view SET b = 20 WHERE a = 0; -- not pushed down - QUERY PLAN --------------------------------------------------------------------------------------------------- +INSERT INTO rw_view VALUES (0, 15); + QUERY PLAN +-------------------------------------------------------------------------------- + Insert on public.foreign_tbl + Remote SQL: INSERT INTO public.base_tbl(a, b) VALUES ($1, $2) RETURNING a, b + -> Result + Output: 0, 15 +(4 rows) + +INSERT INTO rw_view VALUES (0, 15); -- ok +SELECT * FROM foreign_tbl; + a | b +----+---- + 10 | 15 +(1 row) + +EXPLAIN (VERBOSE, COSTS OFF) +UPDATE rw_view SET b = b + 5; + QUERY PLAN +--------------------------------------------------------------------------------------- Update on public.foreign_tbl - Remote SQL: UPDATE public.base_tbl SET b = $2 WHERE ctid = $1 + Remote SQL: UPDATE public.base_tbl SET b = $2 WHERE ctid = $1 RETURNING a, b -> Foreign Scan on public.foreign_tbl - Output: foreign_tbl.a, 20, foreign_tbl.ctid - Remote SQL: SELECT a, ctid FROM public.base_tbl WHERE ((a < b)) AND ((a = 0)) FOR UPDATE + Output: foreign_tbl.a, (foreign_tbl.b + 5), foreign_tbl.ctid + Remote SQL: SELECT a, b, ctid FROM public.base_tbl WHERE ((a < b)) FOR UPDATE (5 rows) -UPDATE rw_view SET b = 20 WHERE a = 0; -- ok +UPDATE rw_view SET b = b + 5; -- should fail +ERROR: new row violates check option for view "rw_view" +DETAIL: Failing row contains (20, 20). EXPLAIN (VERBOSE, COSTS OFF) -UPDATE rw_view SET b = -20 WHERE a = 0; -- not pushed down - QUERY PLAN --------------------------------------------------------------------------------------------------- +UPDATE rw_view SET b = b + 15; + QUERY PLAN +--------------------------------------------------------------------------------------- Update on public.foreign_tbl - Remote SQL: UPDATE public.base_tbl SET b = $2 WHERE ctid = $1 + Remote SQL: UPDATE public.base_tbl SET b = $2 WHERE ctid = $1 RETURNING a, b -> Foreign Scan on public.foreign_tbl - Output: foreign_tbl.a, '-20'::integer, foreign_tbl.ctid - Remote SQL: SELECT a, ctid FROM public.base_tbl WHERE ((a < b)) AND ((a = 0)) FOR UPDATE + Output: foreign_tbl.a, (foreign_tbl.b + 15), foreign_tbl.ctid + Remote SQL: SELECT a, b, ctid FROM public.base_tbl WHERE ((a < b)) FOR UPDATE (5 rows) -UPDATE rw_view SET b = -20 WHERE a = 0; -- should fail -ERROR: new row violates check option for view "rw_view" -DETAIL: Failing row contains (0, -20). +UPDATE rw_view SET b = b + 15; -- ok SELECT * FROM foreign_tbl; - a | b ----+---- - 0 | 20 + a | b +----+---- + 20 | 30 (1 row) DROP FOREIGN TABLE foreign_tbl CASCADE; NOTICE: drop cascades to view rw_view +DROP TRIGGER row_before_insupd_trigger ON base_tbl; DROP TABLE base_tbl; +-- test WCO for partitions +CREATE TABLE child_tbl (a int, b int); +ALTER TABLE child_tbl SET (autovacuum_enabled = 'false'); +CREATE TRIGGER row_before_insupd_trigger BEFORE INSERT OR UPDATE ON child_tbl FOR EACH ROW EXECUTE PROCEDURE row_before_insupd_trigfunc(); +CREATE FOREIGN TABLE foreign_tbl (a int, b int) + SERVER loopback OPTIONS (table_name 'child_tbl'); +CREATE TABLE parent_tbl (a int, b int) PARTITION BY RANGE(a); +ALTER TABLE parent_tbl ATTACH PARTITION foreign_tbl FOR VALUES FROM (0) TO (100); +CREATE VIEW rw_view AS SELECT * FROM parent_tbl + WHERE a < b WITH CHECK OPTION; +\d+ rw_view + View "public.rw_view" + Column | Type | Collation | Nullable | Default | Storage | Description +--------+---------+-----------+----------+---------+---------+------------- + a | integer | | | | plain | + b | integer | | | | plain | +View definition: + SELECT parent_tbl.a, + parent_tbl.b + FROM parent_tbl + WHERE parent_tbl.a < parent_tbl.b; +Options: check_option=cascaded + +EXPLAIN (VERBOSE, COSTS OFF) +INSERT INTO rw_view VALUES (0, 5); + QUERY PLAN +----------------------------- + Insert on public.parent_tbl + -> Result + Output: 0, 5 +(3 rows) + +INSERT INTO rw_view VALUES (0, 5); -- should fail +ERROR: new row violates check option for view "rw_view" +DETAIL: Failing row contains (10, 5). +EXPLAIN (VERBOSE, COSTS OFF) +INSERT INTO rw_view VALUES (0, 15); + QUERY PLAN +----------------------------- + Insert on public.parent_tbl + -> Result + Output: 0, 15 +(3 rows) + +INSERT INTO rw_view VALUES (0, 15); -- ok +SELECT * FROM foreign_tbl; + a | b +----+---- + 10 | 15 +(1 row) + +EXPLAIN (VERBOSE, COSTS OFF) +UPDATE rw_view SET b = b + 5; + QUERY PLAN +---------------------------------------------------------------------------------------- + Update on public.parent_tbl + Foreign Update on public.foreign_tbl + Remote SQL: UPDATE public.child_tbl SET b = $2 WHERE ctid = $1 RETURNING a, b + -> Foreign Scan on public.foreign_tbl + Output: foreign_tbl.a, (foreign_tbl.b + 5), foreign_tbl.ctid + Remote SQL: SELECT a, b, ctid FROM public.child_tbl WHERE ((a < b)) FOR UPDATE +(6 rows) + +UPDATE rw_view SET b = b + 5; -- should fail +ERROR: new row violates check option for view "rw_view" +DETAIL: Failing row contains (20, 20). +EXPLAIN (VERBOSE, COSTS OFF) +UPDATE rw_view SET b = b + 15; + QUERY PLAN +---------------------------------------------------------------------------------------- + Update on public.parent_tbl + Foreign Update on public.foreign_tbl + Remote SQL: UPDATE public.child_tbl SET b = $2 WHERE ctid = $1 RETURNING a, b + -> Foreign Scan on public.foreign_tbl + Output: foreign_tbl.a, (foreign_tbl.b + 15), foreign_tbl.ctid + Remote SQL: SELECT a, b, ctid FROM public.child_tbl WHERE ((a < b)) FOR UPDATE +(6 rows) + +UPDATE rw_view SET b = b + 15; -- ok +SELECT * FROM foreign_tbl; + a | b +----+---- + 20 | 30 +(1 row) + +DROP FOREIGN TABLE foreign_tbl CASCADE; +DROP TRIGGER row_before_insupd_trigger ON child_tbl; +DROP TABLE parent_tbl CASCADE; +NOTICE: drop cascades to view rw_view +DROP FUNCTION row_before_insupd_trigfunc; -- =================================================================== -- test serial columns (ie, sequence-based defaults) -- =================================================================== diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index 9369cfc265..5699252091 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -1582,6 +1582,7 @@ postgresPlanForeignModify(PlannerInfo *root, Relation rel; StringInfoData sql; List *targetAttrs = NIL; + List *withCheckOptionList = NIL; List *returningList = NIL; List *retrieved_attrs = NIL; bool doNothing = false; @@ -1630,6 +1631,13 @@ postgresPlanForeignModify(PlannerInfo *root, } } + /* + * Extract the relevant WITH CHECK OPTION list if any. + */ + if (plan->withCheckOptionLists) + withCheckOptionList = (List *) list_nth(plan->withCheckOptionLists, + subplan_index); + /* * Extract the relevant RETURNING list if any. */ @@ -1655,12 +1663,14 @@ postgresPlanForeignModify(PlannerInfo *root, { case CMD_INSERT: deparseInsertSql(&sql, rte, resultRelation, rel, - targetAttrs, doNothing, returningList, + targetAttrs, doNothing, + withCheckOptionList, returningList, &retrieved_attrs); break; case CMD_UPDATE: deparseUpdateSql(&sql, rte, resultRelation, rel, - targetAttrs, returningList, + targetAttrs, + withCheckOptionList, returningList, &retrieved_attrs); break; case CMD_DELETE: @@ -2046,7 +2056,9 @@ postgresBeginForeignInsert(ModifyTableState *mtstate, /* Construct the SQL command string. */ deparseInsertSql(&sql, rte, resultRelation, rel, targetAttrs, doNothing, - resultRelInfo->ri_returningList, &retrieved_attrs); + resultRelInfo->ri_WithCheckOptions, + resultRelInfo->ri_returningList, + &retrieved_attrs); /* Construct an execution state. */ fmstate = create_foreign_modify(mtstate->ps.state, diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h index a5d4011e8d..70b538e2f9 100644 --- a/contrib/postgres_fdw/postgres_fdw.h +++ b/contrib/postgres_fdw/postgres_fdw.h @@ -142,11 +142,13 @@ extern bool is_foreign_expr(PlannerInfo *root, Expr *expr); extern void deparseInsertSql(StringInfo buf, RangeTblEntry *rte, Index rtindex, Relation rel, - List *targetAttrs, bool doNothing, List *returningList, + List *targetAttrs, bool doNothing, + List *withCheckOptionList, List *returningList, List **retrieved_attrs); extern void deparseUpdateSql(StringInfo buf, RangeTblEntry *rte, Index rtindex, Relation rel, - List *targetAttrs, List *returningList, + List *targetAttrs, + List *withCheckOptionList, List *returningList, List **retrieved_attrs); extern void deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root, Index rtindex, Relation rel, diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index cdfd9c960e..e1b955f3f0 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -1262,27 +1262,74 @@ ALTER FOREIGN TABLE ft1 DROP CONSTRAINT ft1_c2negative; -- test WITH CHECK OPTION constraints -- =================================================================== +CREATE FUNCTION row_before_insupd_trigfunc() RETURNS trigger AS $$BEGIN NEW.a := NEW.a + 10; RETURN NEW; END$$ LANGUAGE plpgsql; + CREATE TABLE base_tbl (a int, b int); ALTER TABLE base_tbl SET (autovacuum_enabled = 'false'); +CREATE TRIGGER row_before_insupd_trigger BEFORE INSERT OR UPDATE ON base_tbl FOR EACH ROW EXECUTE PROCEDURE row_before_insupd_trigfunc(); CREATE FOREIGN TABLE foreign_tbl (a int, b int) - SERVER loopback OPTIONS(table_name 'base_tbl'); + SERVER loopback OPTIONS (table_name 'base_tbl'); CREATE VIEW rw_view AS SELECT * FROM foreign_tbl WHERE a < b WITH CHECK OPTION; \d+ rw_view -INSERT INTO rw_view VALUES (0, 10); -- ok -INSERT INTO rw_view VALUES (10, 0); -- should fail EXPLAIN (VERBOSE, COSTS OFF) -UPDATE rw_view SET b = 20 WHERE a = 0; -- not pushed down -UPDATE rw_view SET b = 20 WHERE a = 0; -- ok +INSERT INTO rw_view VALUES (0, 5); +INSERT INTO rw_view VALUES (0, 5); -- should fail +EXPLAIN (VERBOSE, COSTS OFF) +INSERT INTO rw_view VALUES (0, 15); +INSERT INTO rw_view VALUES (0, 15); -- ok +SELECT * FROM foreign_tbl; + +EXPLAIN (VERBOSE, COSTS OFF) +UPDATE rw_view SET b = b + 5; +UPDATE rw_view SET b = b + 5; -- should fail EXPLAIN (VERBOSE, COSTS OFF) -UPDATE rw_view SET b = -20 WHERE a = 0; -- not pushed down -UPDATE rw_view SET b = -20 WHERE a = 0; -- should fail +UPDATE rw_view SET b = b + 15; +UPDATE rw_view SET b = b + 15; -- ok SELECT * FROM foreign_tbl; DROP FOREIGN TABLE foreign_tbl CASCADE; +DROP TRIGGER row_before_insupd_trigger ON base_tbl; DROP TABLE base_tbl; +-- test WCO for partitions + +CREATE TABLE child_tbl (a int, b int); +ALTER TABLE child_tbl SET (autovacuum_enabled = 'false'); +CREATE TRIGGER row_before_insupd_trigger BEFORE INSERT OR UPDATE ON child_tbl FOR EACH ROW EXECUTE PROCEDURE row_before_insupd_trigfunc(); +CREATE FOREIGN TABLE foreign_tbl (a int, b int) + SERVER loopback OPTIONS (table_name 'child_tbl'); + +CREATE TABLE parent_tbl (a int, b int) PARTITION BY RANGE(a); +ALTER TABLE parent_tbl ATTACH PARTITION foreign_tbl FOR VALUES FROM (0) TO (100); + +CREATE VIEW rw_view AS SELECT * FROM parent_tbl + WHERE a < b WITH CHECK OPTION; +\d+ rw_view + +EXPLAIN (VERBOSE, COSTS OFF) +INSERT INTO rw_view VALUES (0, 5); +INSERT INTO rw_view VALUES (0, 5); -- should fail +EXPLAIN (VERBOSE, COSTS OFF) +INSERT INTO rw_view VALUES (0, 15); +INSERT INTO rw_view VALUES (0, 15); -- ok +SELECT * FROM foreign_tbl; + +EXPLAIN (VERBOSE, COSTS OFF) +UPDATE rw_view SET b = b + 5; +UPDATE rw_view SET b = b + 5; -- should fail +EXPLAIN (VERBOSE, COSTS OFF) +UPDATE rw_view SET b = b + 15; +UPDATE rw_view SET b = b + 15; -- ok +SELECT * FROM foreign_tbl; + +DROP FOREIGN TABLE foreign_tbl CASCADE; +DROP TRIGGER row_before_insupd_trigger ON child_tbl; +DROP TABLE parent_tbl CASCADE; + +DROP FUNCTION row_before_insupd_trigfunc; + -- =================================================================== -- test serial columns (ie, sequence-based defaults) -- =================================================================== diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml index 7b758bdf09..4ce88dd77c 100644 --- a/doc/src/sgml/fdwhandler.sgml +++ b/doc/src/sgml/fdwhandler.sgml @@ -573,12 +573,14 @@ ExecForeignInsert(EState *estate, The data in the returned slot is used only if the INSERT - query has a RETURNING clause or the foreign table has - an AFTER ROW trigger. Triggers require all columns, but the - FDW could choose to optimize away returning some or all columns depending - on the contents of the RETURNING clause. Regardless, some - slot must be returned to indicate success, or the query's reported row - count will be wrong. + statement has a RETURNING clause or involves a view + WITH CHECK OPTION; or if the foreign table has + an AFTER ROW trigger. Triggers require all columns, + but the FDW could choose to optimize away returning some or all columns + depending on the contents of the RETURNING clause or + WITH CHECK OPTION constraints. Regardless, some slot + must be returned to indicate success, or the query's reported row count + will be wrong. @@ -619,12 +621,14 @@ ExecForeignUpdate(EState *estate, The data in the returned slot is used only if the UPDATE - query has a RETURNING clause or the foreign table has - an AFTER ROW trigger. Triggers require all columns, but the - FDW could choose to optimize away returning some or all columns depending - on the contents of the RETURNING clause. Regardless, some - slot must be returned to indicate success, or the query's reported row - count will be wrong. + statement has a RETURNING clause or involves a view + WITH CHECK OPTION; or if the foreign table has + an AFTER ROW trigger. Triggers require all columns, + but the FDW could choose to optimize away returning some or all columns + depending on the contents of the RETURNING clause or + WITH CHECK OPTION constraints. Regardless, some slot + must be returned to indicate success, or the query's reported row count + will be wrong.