#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
+#include "access/sysattr.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/objectaccess.h"
return conOid;
}
+/*
+ * get_primary_key_attnos
+ * Identify the columns in a relation's primary key, if any.
+ *
+ * Returns a Bitmapset of the column attnos of the primary key's columns,
+ * with attnos being offset by FirstLowInvalidHeapAttributeNumber so that
+ * system columns can be represented.
+ *
+ * If there is no primary key, return NULL. We also return NULL if the pkey
+ * constraint is deferrable and deferrableOk is false.
+ *
+ * *constraintOid is set to the OID of the pkey constraint, or InvalidOid
+ * on failure.
+ */
+Bitmapset *
+get_primary_key_attnos(Oid relid, bool deferrableOk, Oid *constraintOid)
+{
+ Bitmapset *pkattnos = NULL;
+ Relation pg_constraint;
+ HeapTuple tuple;
+ SysScanDesc scan;
+ ScanKeyData skey[1];
+
+ /* Set *constraintOid, to avoid complaints about uninitialized vars */
+ *constraintOid = InvalidOid;
+
+ /* Scan pg_constraint for constraints of the target rel */
+ pg_constraint = heap_open(ConstraintRelationId, AccessShareLock);
+
+ ScanKeyInit(&skey[0],
+ Anum_pg_constraint_conrelid,
+ BTEqualStrategyNumber, F_OIDEQ,
+ ObjectIdGetDatum(relid));
+
+ scan = systable_beginscan(pg_constraint, ConstraintRelidIndexId, true,
+ NULL, 1, skey);
+
+ while (HeapTupleIsValid(tuple = systable_getnext(scan)))
+ {
+ Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
+ Datum adatum;
+ bool isNull;
+ ArrayType *arr;
+ int16 *attnums;
+ int numkeys;
+ int i;
+
+ /* Skip constraints that are not PRIMARY KEYs */
+ if (con->contype != CONSTRAINT_PRIMARY)
+ continue;
+
+ /*
+ * If the primary key is deferrable, but we've been instructed to
+ * ignore deferrable constraints, then we might as well give up
+ * searching, since there can only be a single primary key on a table.
+ */
+ if (con->condeferrable && !deferrableOk)
+ break;
+
+ /* Extract the conkey array, ie, attnums of PK's columns */
+ adatum = heap_getattr(tuple, Anum_pg_constraint_conkey,
+ RelationGetDescr(pg_constraint), &isNull);
+ if (isNull)
+ elog(ERROR, "null conkey for constraint %u",
+ HeapTupleGetOid(tuple));
+ arr = DatumGetArrayTypeP(adatum); /* ensure not toasted */
+ numkeys = ARR_DIMS(arr)[0];
+ if (ARR_NDIM(arr) != 1 ||
+ numkeys < 0 ||
+ ARR_HASNULL(arr) ||
+ ARR_ELEMTYPE(arr) != INT2OID)
+ elog(ERROR, "conkey is not a 1-D smallint array");
+ attnums = (int16 *) ARR_DATA_PTR(arr);
+
+ /* Construct the result value */
+ for (i = 0; i < numkeys; i++)
+ {
+ pkattnos = bms_add_member(pkattnos,
+ attnums[i] - FirstLowInvalidHeapAttributeNumber);
+ }
+ *constraintOid = HeapTupleGetOid(tuple);
+
+ /* No need to search further */
+ break;
+ }
+
+ systable_endscan(scan);
+
+ heap_close(pg_constraint, AccessShareLock);
+
+ return pkattnos;
+}
+
/*
* Determine whether a relation can be proven functionally dependent on
* a set of grouping columns. If so, return TRUE and add the pg_constraint
#include "access/htup_details.h"
#include "access/parallel.h"
+#include "access/sysattr.h"
#include "access/xact.h"
+#include "catalog/pg_constraint_fn.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "foreign/fdwapi.h"
double tuple_fraction,
int64 *offset_est, int64 *count_est);
static bool limit_needed(Query *parse);
+static void remove_useless_groupby_columns(PlannerInfo *root);
static List *preprocess_groupclause(PlannerInfo *root, List *force);
static List *extract_rollup_sets(List *groupingSets);
static List *reorder_grouping_sets(List *groupingSets, List *sortclause);
}
parse->havingQual = (Node *) newHaving;
+ /* Remove any redundant GROUP BY columns */
+ remove_useless_groupby_columns(root);
+
/*
* If we have any outer joins, try to reduce them to plain inner joins.
* This step is most easily done after we've done expression
}
+/*
+ * remove_useless_groupby_columns
+ * Remove any columns in the GROUP BY clause that are redundant due to
+ * being functionally dependent on other GROUP BY columns.
+ *
+ * Since some other DBMSes do not allow references to ungrouped columns, it's
+ * not unusual to find all columns listed in GROUP BY even though listing the
+ * primary-key columns would be sufficient. Deleting such excess columns
+ * avoids redundant sorting work, so it's worth doing. When we do this, we
+ * must mark the plan as dependent on the pkey constraint (compare the
+ * parser's check_ungrouped_columns() and check_functional_grouping()).
+ *
+ * In principle, we could treat any NOT-NULL columns appearing in a UNIQUE
+ * index as the determining columns. But as with check_functional_grouping(),
+ * there's currently no way to represent dependency on a NOT NULL constraint,
+ * so we consider only the pkey for now.
+ */
+static void
+remove_useless_groupby_columns(PlannerInfo *root)
+{
+ Query *parse = root->parse;
+ Bitmapset **groupbyattnos;
+ Bitmapset **surplusvars;
+ ListCell *lc;
+ int relid;
+
+ /* No chance to do anything if there are less than two GROUP BY items */
+ if (list_length(parse->groupClause) < 2)
+ return;
+
+ /* Don't fiddle with the GROUP BY clause if the query has grouping sets */
+ if (parse->groupingSets)
+ return;
+
+ /*
+ * Scan the GROUP BY clause to find GROUP BY items that are simple Vars.
+ * Fill groupbyattnos[k] with a bitmapset of the column attnos of RTE k
+ * that are GROUP BY items.
+ */
+ groupbyattnos = (Bitmapset **) palloc0(sizeof(Bitmapset *) *
+ (list_length(parse->rtable) + 1));
+ foreach(lc, parse->groupClause)
+ {
+ SortGroupClause *sgc = (SortGroupClause *) lfirst(lc);
+ TargetEntry *tle = get_sortgroupclause_tle(sgc, parse->targetList);
+ Var *var = (Var *) tle->expr;
+
+ /*
+ * Ignore non-Vars and Vars from other query levels.
+ *
+ * XXX in principle, stable expressions containing Vars could also be
+ * removed, if all the Vars are functionally dependent on other GROUP
+ * BY items. But it's not clear that such cases occur often enough to
+ * be worth troubling over.
+ */
+ if (!IsA(var, Var) ||
+ var->varlevelsup > 0)
+ continue;
+
+ /* OK, remember we have this Var */
+ relid = var->varno;
+ Assert(relid <= list_length(parse->rtable));
+ groupbyattnos[relid] = bms_add_member(groupbyattnos[relid],
+ var->varattno - FirstLowInvalidHeapAttributeNumber);
+ }
+
+ /*
+ * Consider each relation and see if it is possible to remove some of its
+ * Vars from GROUP BY. For simplicity and speed, we do the actual removal
+ * in a separate pass. Here, we just fill surplusvars[k] with a bitmapset
+ * of the column attnos of RTE k that are removable GROUP BY items.
+ */
+ surplusvars = NULL; /* don't allocate array unless required */
+ relid = 0;
+ foreach(lc, parse->rtable)
+ {
+ RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);
+ Bitmapset *relattnos;
+ Bitmapset *pkattnos;
+ Oid constraintOid;
+
+ relid++;
+
+ /* Only plain relations could have primary-key constraints */
+ if (rte->rtekind != RTE_RELATION)
+ continue;
+
+ /* Nothing to do unless this rel has multiple Vars in GROUP BY */
+ relattnos = groupbyattnos[relid];
+ if (bms_membership(relattnos) != BMS_MULTIPLE)
+ continue;
+
+ /*
+ * Can't remove any columns for this rel if there is no suitable
+ * (i.e., nondeferrable) primary key constraint.
+ */
+ pkattnos = get_primary_key_attnos(rte->relid, false, &constraintOid);
+ if (pkattnos == NULL)
+ continue;
+
+ /*
+ * If the primary key is a proper subset of relattnos then we have
+ * some items in the GROUP BY that can be removed.
+ */
+ if (bms_subset_compare(pkattnos, relattnos) == BMS_SUBSET1)
+ {
+ /*
+ * To easily remember whether we've found anything to do, we don't
+ * allocate the surplusvars[] array until we find something.
+ */
+ if (surplusvars == NULL)
+ surplusvars = (Bitmapset **) palloc0(sizeof(Bitmapset *) *
+ (list_length(parse->rtable) + 1));
+
+ /* Remember the attnos of the removable columns */
+ surplusvars[relid] = bms_difference(relattnos, pkattnos);
+
+ /* Also, mark the resulting plan as dependent on this constraint */
+ parse->constraintDeps = lappend_oid(parse->constraintDeps,
+ constraintOid);
+ }
+ }
+
+ /*
+ * If we found any surplus Vars, build a new GROUP BY clause without them.
+ * (Note: this may leave some TLEs with unreferenced ressortgroupref
+ * markings, but that's harmless.)
+ */
+ if (surplusvars != NULL)
+ {
+ List *new_groupby = NIL;
+
+ foreach(lc, parse->groupClause)
+ {
+ SortGroupClause *sgc = (SortGroupClause *) lfirst(lc);
+ TargetEntry *tle = get_sortgroupclause_tle(sgc, parse->targetList);
+ Var *var = (Var *) tle->expr;
+
+ /*
+ * New list must include non-Vars, outer Vars, and anything not
+ * marked as surplus.
+ */
+ if (!IsA(var, Var) ||
+ var->varlevelsup > 0 ||
+ !bms_is_member(var->varattno - FirstLowInvalidHeapAttributeNumber,
+ surplusvars[var->varno]))
+ new_groupby = lappend(new_groupby, sgc);
+ }
+
+ parse->groupClause = new_groupby;
+ }
+}
+
/*
* preprocess_groupclause - do preparatory work on GROUP BY clause
*
extern Oid get_relation_constraint_oid(Oid relid, const char *conname, bool missing_ok);
extern Oid get_domain_constraint_oid(Oid typid, const char *conname, bool missing_ok);
+extern Bitmapset *get_primary_key_attnos(Oid relid, bool deferrableOk,
+ Oid *constraintOid);
+
extern bool check_functional_grouping(Oid relid,
Index varno, Index varlevelsup,
List *grouping_columns,
LINE 1: select (select max(min(unique1)) from int8_tbl) from tenk1;
^
--
+-- Test removal of redundant GROUP BY columns
+--
+create temp table t1 (a int, b int, c int, d int, primary key (a, b));
+create temp table t2 (x int, y int, z int, primary key (x, y));
+create temp table t3 (a int, b int, c int, primary key(a, b) deferrable);
+-- Non-primary-key columns can be removed from GROUP BY
+explain (costs off) select * from t1 group by a,b,c,d;
+ QUERY PLAN
+----------------------
+ HashAggregate
+ Group Key: a, b
+ -> Seq Scan on t1
+(3 rows)
+
+-- No removal can happen if the complete PK is not present in GROUP BY
+explain (costs off) select a,c from t1 group by a,c,d;
+ QUERY PLAN
+----------------------
+ HashAggregate
+ Group Key: a, c, d
+ -> Seq Scan on t1
+(3 rows)
+
+-- Test removal across multiple relations
+explain (costs off) select *
+from t1 inner join t2 on t1.a = t2.x and t1.b = t2.y
+group by t1.a,t1.b,t1.c,t1.d,t2.x,t2.y,t2.z;
+ QUERY PLAN
+-------------------------------------------------------
+ Group
+ Group Key: t1.a, t1.b, t2.x, t2.y
+ -> Merge Join
+ Merge Cond: ((t1.a = t2.x) AND (t1.b = t2.y))
+ -> Index Scan using t1_pkey on t1
+ -> Index Scan using t2_pkey on t2
+(6 rows)
+
+-- Test case where t1 can be optimized but not t2
+explain (costs off) select t1.*,t2.x,t2.z
+from t1 inner join t2 on t1.a = t2.x and t1.b = t2.y
+group by t1.a,t1.b,t1.c,t1.d,t2.x,t2.z;
+ QUERY PLAN
+-------------------------------------------------------
+ HashAggregate
+ Group Key: t1.a, t1.b, t2.x, t2.z
+ -> Merge Join
+ Merge Cond: ((t1.a = t2.x) AND (t1.b = t2.y))
+ -> Index Scan using t1_pkey on t1
+ -> Index Scan using t2_pkey on t2
+(6 rows)
+
+-- Cannot optimize when PK is deferrable
+explain (costs off) select * from t3 group by a,b,c;
+ QUERY PLAN
+----------------------
+ HashAggregate
+ Group Key: a, b, c
+ -> Seq Scan on t3
+(3 rows)
+
+drop table t1;
+drop table t2;
+drop table t3;
+--
-- Test combinations of DISTINCT and/or ORDER BY
--
select array_agg(a order by b)
(1 row)
-- join removal is not possible when the GROUP BY contains a column that is
--- not in the join condition
+-- not in the join condition. (Note: as of 9.6, we notice that b.id is a
+-- primary key and so drop b.c_id from the GROUP BY of the resulting plan;
+-- but this happens too late for join removal in the outer plan level.)
explain (costs off)
select d.* from d left join (select * from b group by b.id, b.c_id) s
on d.a = s.id;
- QUERY PLAN
----------------------------------------------
+ QUERY PLAN
+---------------------------------------
Merge Left Join
Merge Cond: (d.a = s.id)
-> Sort
Sort Key: s.id
-> Subquery Scan on s
-> HashAggregate
- Group Key: b.id, b.c_id
+ Group Key: b.id
-> Seq Scan on b
(11 rows)
select max(min(unique1)) from tenk1;
select (select max(min(unique1)) from int8_tbl) from tenk1;
+--
+-- Test removal of redundant GROUP BY columns
+--
+
+create temp table t1 (a int, b int, c int, d int, primary key (a, b));
+create temp table t2 (x int, y int, z int, primary key (x, y));
+create temp table t3 (a int, b int, c int, primary key(a, b) deferrable);
+
+-- Non-primary-key columns can be removed from GROUP BY
+explain (costs off) select * from t1 group by a,b,c,d;
+
+-- No removal can happen if the complete PK is not present in GROUP BY
+explain (costs off) select a,c from t1 group by a,c,d;
+
+-- Test removal across multiple relations
+explain (costs off) select *
+from t1 inner join t2 on t1.a = t2.x and t1.b = t2.y
+group by t1.a,t1.b,t1.c,t1.d,t2.x,t2.y,t2.z;
+
+-- Test case where t1 can be optimized but not t2
+explain (costs off) select t1.*,t2.x,t2.z
+from t1 inner join t2 on t1.a = t2.x and t1.b = t2.y
+group by t1.a,t1.b,t1.c,t1.d,t2.x,t2.z;
+
+-- Cannot optimize when PK is deferrable
+explain (costs off) select * from t3 group by a,b,c;
+
+drop table t1;
+drop table t2;
+drop table t3;
+
--
-- Test combinations of DISTINCT and/or ORDER BY
--
on d.a = s.id and d.b = s.c_id;
-- join removal is not possible when the GROUP BY contains a column that is
--- not in the join condition
+-- not in the join condition. (Note: as of 9.6, we notice that b.id is a
+-- primary key and so drop b.c_id from the GROUP BY of the resulting plan;
+-- but this happens too late for join removal in the outer plan level.)
explain (costs off)
select d.* from d left join (select * from b group by b.id, b.c_id) s
on d.a = s.id;
projects / postgresql / commitdiff