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Implement GROUP BY DISTINCT

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With grouping sets, it's possible that some of the grouping sets are
duplicate.  This is especially common with CUBE and ROLLUP clauses. For
example GROUP BY CUBE (a,b), CUBE (b,c) is equivalent to

  GROUP BY GROUPING SETS (
    (a, b, c),
    (a, b, c),
    (a, b, c),
    (a, b),
    (a, b),
    (a, b),
    (a),
    (a),
    (a),
    (c, a),
    (c, a),
    (c, a),
    (c),
    (b, c),
    (b),
    ()
  )

Some of the grouping sets are calculated multiple times, which is mostly
unnecessary.  This commit implements a new GROUP BY DISTINCT feature, as
defined in the SQL standard, which eliminates the duplicate sets.

Author: Vik Fearing
Reviewed-by: Erik Rijkers, Georgios Kokolatos, Tomas Vondra
Discussion: https://postgr.es/m/bf3805a8-d7d1-ae61-fece-761b7ff41ecc@postgresfriends.org
This commit is contained in:
Tomas Vondra 2021-03-18 17:45:38 +01:00
parent cd91de0d17
commit be45be9c33
18 changed files with 333 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

54
doc/src/sgml/queries.sgml
View File

@ -1372,6 +1372,55 @@ GROUP BY GROUPING SETS (
</programlisting>
</para>
<para>
<indexterm zone="queries-grouping-sets">
<primary>ALL</primary>
<secondary>GROUP BY ALL</secondary>
</indexterm>
<indexterm zone="queries-grouping-sets">
<primary>DISTINCT</primary>
<secondary>GROUP BY DISTINCT</secondary>
</indexterm>
When specifying multiple grouping items together, the final set of grouping
sets might contain duplicates. For example:
<programlisting>
GROUP BY ROLLUP (a, b), ROLLUP (a, c)
</programlisting>
is equivalent to
<programlisting>
GROUP BY GROUPING SETS (
(a, b, c),
(a, b),
(a, b),
(a, c),
(a),
(a),
(a, c),
(a),
()
)
</programlisting>
If these duplicates are undesirable, they can be removed using the
<literal>DISTINCT</literal> clause directly on the <literal>GROUP BY</literal>.
Therefore:
<programlisting>
GROUP BY <emphasis>DISTINCT</emphasis> ROLLUP (a, b), ROLLUP (a, c)
</programlisting>
is equivalent to
<programlisting>
GROUP BY GROUPING SETS (
(a, b, c),
(a, b),
(a, c),
(a),
()
)
</programlisting>
This is not the same as using <literal>SELECT DISTINCT</literal> because the output
rows may still contain duplicates. If any of the ungrouped columns contains NULL,
it will be indistinguishable from the NULL used when that same column is grouped.
</para>
<note>
<para>
The construct <literal>(a, b)</literal> is normally recognized in expressions as
@ -1560,8 +1609,13 @@ SELECT a "from", b + c AS sum FROM ...
<sect2 id="queries-distinct">
<title><literal>DISTINCT</literal></title>
<indexterm zone="queries-distinct">
<primary>ALL</primary>
<secondary>SELECT ALL</secondary>
</indexterm>
<indexterm zone="queries-distinct">
<primary>DISTINCT</primary>
<secondary>SELECT DISTINCT</secondary>
</indexterm>
<indexterm zone="queries-distinct">

9
doc/src/sgml/ref/select.sgml
View File

@ -37,7 +37,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
[ * | <replaceable class="parameter">expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
[ FROM <replaceable class="parameter">from_item</replaceable> [, ...] ]
[ WHERE <replaceable class="parameter">condition</replaceable> ]
[ GROUP BY <replaceable class="parameter">grouping_element</replaceable> [, ...] ]
[ GROUP BY [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</replaceable> [, ...] ]
[ HAVING <replaceable class="parameter">condition</replaceable> ]
[ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceable class="parameter">window_definition</replaceable> ) [, ...] ]
[ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] <replaceable class="parameter">select</replaceable> ]
@ -778,7 +778,7 @@ WHERE <replaceable class="parameter">condition</replaceable>
<para>
The optional <literal>GROUP BY</literal> clause has the general form
<synopsis>
GROUP BY <replaceable class="parameter">grouping_element</replaceable> [, ...]
GROUP BY [ ALL | DISTINCT ] <replaceable class="parameter">grouping_element</replaceable> [, ...]
</synopsis>
</para>
@ -802,7 +802,10 @@ GROUP BY <replaceable class="parameter">grouping_element</replaceable> [, ...]
independent <replaceable>grouping sets</replaceable>. The effect of this is
equivalent to constructing a <literal>UNION ALL</literal> between
subqueries with the individual grouping sets as their
<literal>GROUP BY</literal> clauses. For further details on the handling
<literal>GROUP BY</literal> clauses. The optional <literal>DISTINCT</literal>
clause removes duplicate sets before processing; it does <emphasis>not</emphasis>
transform the <literal>UNION ALL</literal> into a <literal>UNION DISTINCT</literal>.
For further details on the handling
of grouping sets see <xref linkend="queries-grouping-sets"/>.
</para>

2
src/backend/catalog/sql_features.txt
View File

@ -482,7 +482,7 @@ T351 Bracketed SQL comments (/*...*/ comments) YES
T431 Extended grouping capabilities YES
T432 Nested and concatenated GROUPING SETS YES
T433 Multiargument GROUPING function YES
T434 GROUP BY DISTINCT NO
T434 GROUP BY DISTINCT YES
T441 ABS and MOD functions YES
T461 Symmetric BETWEEN predicate YES
T471 Result sets return value NO

2
src/backend/nodes/copyfuncs.c
View File

@ -3135,6 +3135,7 @@ _copyQuery(const Query *from)
COPY_NODE_FIELD(onConflict);
COPY_NODE_FIELD(returningList);
COPY_NODE_FIELD(groupClause);
COPY_SCALAR_FIELD(groupDistinct);
COPY_NODE_FIELD(groupingSets);
COPY_NODE_FIELD(havingQual);
COPY_NODE_FIELD(windowClause);
@ -3221,6 +3222,7 @@ _copySelectStmt(const SelectStmt *from)
COPY_NODE_FIELD(fromClause);
COPY_NODE_FIELD(whereClause);
COPY_NODE_FIELD(groupClause);
COPY_SCALAR_FIELD(groupDistinct);
COPY_NODE_FIELD(havingClause);
COPY_NODE_FIELD(windowClause);
COPY_NODE_FIELD(valuesLists);

2
src/backend/nodes/equalfuncs.c
View File

@ -977,6 +977,7 @@ _equalQuery(const Query *a, const Query *b)
COMPARE_NODE_FIELD(onConflict);
COMPARE_NODE_FIELD(returningList);
COMPARE_NODE_FIELD(groupClause);
COMPARE_SCALAR_FIELD(groupDistinct);
COMPARE_NODE_FIELD(groupingSets);
COMPARE_NODE_FIELD(havingQual);
COMPARE_NODE_FIELD(windowClause);
@ -1053,6 +1054,7 @@ _equalSelectStmt(const SelectStmt *a, const SelectStmt *b)
COMPARE_NODE_FIELD(fromClause);
COMPARE_NODE_FIELD(whereClause);
COMPARE_NODE_FIELD(groupClause);
COMPARE_SCALAR_FIELD(groupDistinct);
COMPARE_NODE_FIELD(havingClause);
COMPARE_NODE_FIELD(windowClause);
COMPARE_NODE_FIELD(valuesLists);

16
src/backend/nodes/list.c
View File

@ -1506,6 +1506,22 @@ list_sort(List *list, list_sort_comparator cmp)
qsort(list->elements, len, sizeof(ListCell), (qsort_comparator) cmp);
}
/*
* list_sort comparator for sorting a list into ascending int order.
*/
int
list_int_cmp(const ListCell *p1, const ListCell *p2)
{
int v1 = lfirst_int(p1);
int v2 = lfirst_int(p2);
if (v1 < v2)
return -1;
if (v1 > v2)
return 1;
return 0;
}
/*
* list_sort comparator for sorting a list into ascending OID order.
*/

2
src/backend/nodes/outfuncs.c
View File

@ -2771,6 +2771,7 @@ _outSelectStmt(StringInfo str, const SelectStmt *node)
WRITE_NODE_FIELD(fromClause);
WRITE_NODE_FIELD(whereClause);
WRITE_NODE_FIELD(groupClause);
WRITE_BOOL_FIELD(groupDistinct);
WRITE_NODE_FIELD(havingClause);
WRITE_NODE_FIELD(windowClause);
WRITE_NODE_FIELD(valuesLists);
@ -2996,6 +2997,7 @@ _outQuery(StringInfo str, const Query *node)
WRITE_NODE_FIELD(onConflict);
WRITE_NODE_FIELD(returningList);
WRITE_NODE_FIELD(groupClause);
WRITE_BOOL_FIELD(groupDistinct);
WRITE_NODE_FIELD(groupingSets);
WRITE_NODE_FIELD(havingQual);
WRITE_NODE_FIELD(windowClause);

1
src/backend/nodes/readfuncs.c
View File

@ -271,6 +271,7 @@ _readQuery(void)
READ_NODE_FIELD(onConflict);
READ_NODE_FIELD(returningList);
READ_NODE_FIELD(groupClause);
READ_BOOL_FIELD(groupDistinct);
READ_NODE_FIELD(groupingSets);
READ_NODE_FIELD(havingQual);
READ_NODE_FIELD(windowClause);

2
src/backend/optimizer/plan/planner.c
View File

@ -2442,7 +2442,7 @@ preprocess_grouping_sets(PlannerInfo *root)
ListCell *lc_set;
grouping_sets_data *gd = palloc0(sizeof(grouping_sets_data));
parse->groupingSets = expand_grouping_sets(parse->groupingSets, -1);
parse->groupingSets = expand_grouping_sets(parse->groupingSets, parse->groupDistinct, -1);
gd->any_hashable = false;
gd->unhashable_refs = NULL;

1
src/backend/parser/analyze.c
View File

@ -1264,6 +1264,7 @@ transformSelectStmt(ParseState *pstate, SelectStmt *stmt)
qry->sortClause,
EXPR_KIND_GROUP_BY,
false /* allow SQL92 rules */ );
qry->groupDistinct = stmt->groupDistinct;
if (stmt->distinctClause == NIL)
{

59
src/backend/parser/gram.y
View File

@ -134,6 +134,13 @@ typedef struct SelectLimit
LimitOption limitOption;
} SelectLimit;
/* Private struct for the result of group_clause production */
typedef struct GroupClause
{
bool distinct;
List *list;
} GroupClause;
/* ConstraintAttributeSpec yields an integer bitmask of these flags: */
#define CAS_NOT_DEFERRABLE 0x01
#define CAS_DEFERRABLE 0x02
@ -250,6 +257,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
PartitionBoundSpec *partboundspec;
RoleSpec *rolespec;
struct SelectLimit *selectlimit;
SetQuantifier setquantifier;
struct GroupClause *groupclause;
}
%type <node> stmt schema_stmt
@ -405,7 +414,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
target_list opt_target_list insert_column_list set_target_list
set_clause_list set_clause
def_list operator_def_list indirection opt_indirection
reloption_list group_clause TriggerFuncArgs opclass_item_list opclass_drop_list
reloption_list TriggerFuncArgs opclass_item_list opclass_drop_list
opclass_purpose opt_opfamily transaction_mode_list_or_empty
OptTableFuncElementList TableFuncElementList opt_type_modifiers
prep_type_clause
@ -418,6 +427,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
vacuum_relation_list opt_vacuum_relation_list
drop_option_list
%type <groupclause> group_clause
%type <list> group_by_list
%type <node> group_by_item empty_grouping_set rollup_clause cube_clause
%type <node> grouping_sets_clause
@ -443,7 +453,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
%type <node> for_locking_item
%type <list> for_locking_clause opt_for_locking_clause for_locking_items
%type <list> locked_rels_list
%type <boolean> all_or_distinct
%type <setquantifier> set_quantifier
%type <node> join_qual
%type <jtype> join_type
@ -11294,7 +11304,8 @@ simple_select:
n->intoClause = $4;
n->fromClause = $5;
n->whereClause = $6;
n->groupClause = $7;
n->groupClause = ($7)->list;
n->groupDistinct = ($7)->distinct;
n->havingClause = $8;
n->windowClause = $9;
$$ = (Node *)n;
@ -11309,7 +11320,8 @@ simple_select:
n->intoClause = $4;
n->fromClause = $5;
n->whereClause = $6;
n->groupClause = $7;
n->groupClause = ($7)->list;
n->groupDistinct = ($7)->distinct;
n->havingClause = $8;
n->windowClause = $9;
$$ = (Node *)n;
@ -11334,17 +11346,17 @@ simple_select:
n->fromClause = list_make1($2);
$$ = (Node *)n;
}
| select_clause UNION all_or_distinct select_clause
| select_clause UNION set_quantifier select_clause
{
$$ = makeSetOp(SETOP_UNION, $3, $1, $4);
$$ = makeSetOp(SETOP_UNION, $3 == SET_QUANTIFIER_ALL, $1, $4);
}
| select_clause INTERSECT all_or_distinct select_clause
| select_clause INTERSECT set_quantifier select_clause
{
$$ = makeSetOp(SETOP_INTERSECT, $3, $1, $4);
$$ = makeSetOp(SETOP_INTERSECT, $3 == SET_QUANTIFIER_ALL, $1, $4);
}
| select_clause EXCEPT all_or_distinct select_clause
| select_clause EXCEPT set_quantifier select_clause
{
$$ = makeSetOp(SETOP_EXCEPT, $3, $1, $4);
$$ = makeSetOp(SETOP_EXCEPT, $3 == SET_QUANTIFIER_ALL, $1, $4);
}
;
@ -11542,10 +11554,10 @@ opt_table: TABLE
| /*EMPTY*/
;
all_or_distinct:
ALL { $$ = true; }
| DISTINCT { $$ = false; }
| /*EMPTY*/ { $$ = false; }
set_quantifier:
ALL { $$ = SET_QUANTIFIER_ALL; }
| DISTINCT { $$ = SET_QUANTIFIER_DISTINCT; }
| /*EMPTY*/ { $$ = SET_QUANTIFIER_DEFAULT; }
;
/* We use (NIL) as a placeholder to indicate that all target expressions
@ -11771,8 +11783,20 @@ first_or_next: FIRST_P { $$ = 0; }
* GroupingSet node of some type.
*/
group_clause:
GROUP_P BY group_by_list { $$ = $3; }
| /*EMPTY*/ { $$ = NIL; }
GROUP_P BY set_quantifier group_by_list
{
GroupClause *n = (GroupClause *) palloc(sizeof(GroupClause));
n->distinct = $3 == SET_QUANTIFIER_DISTINCT;
n->list = $4;
$$ = n;
}
| /*EMPTY*/
{
GroupClause *n = (GroupClause *) palloc(sizeof(GroupClause));
n->distinct = false;
n->list = NIL;
$$ = n;
}
;
group_by_list:
@ -15145,7 +15169,8 @@ PLpgSQL_Expr: opt_distinct_clause opt_target_list
n->targetList = $2;
n->fromClause = $3;
n->whereClause = $4;
n->groupClause = $5;
n->groupClause = ($5)->list;
n->groupDistinct = ($5)->distinct;
n->havingClause = $6;
n->windowClause = $7;
n->sortClause = $8;

58
src/backend/parser/parse_agg.c
View File

@ -1071,7 +1071,7 @@ parseCheckAggregates(ParseState *pstate, Query *qry)
* The limit of 4096 is arbitrary and exists simply to avoid resource
* issues from pathological constructs.
*/
List *gsets = expand_grouping_sets(qry->groupingSets, 4096);
List *gsets = expand_grouping_sets(qry->groupingSets, qry->groupDistinct, 4096);
if (!gsets)
ereport(ERROR,
@ -1735,6 +1735,33 @@ cmp_list_len_asc(const ListCell *a, const ListCell *b)
return (la > lb) ? 1 : (la == lb) ? 0 : -1;
}
/* list_sort comparator to sort sub-lists by length and contents */
static int
cmp_list_len_contents_asc(const ListCell *a, const ListCell *b)
{
int res = cmp_list_len_asc(a, b);
if (res == 0)
{
List *la = (List *) lfirst(a);
List *lb = (List *) lfirst(b);
ListCell *lca;
ListCell *lcb;
forboth(lca, la, lcb, lb)
{
int va = intVal(lca);
int vb = intVal(lcb);
if (va > vb)
return 1;
if (va < vb)
return -1;
}
}
return res;
}
/*
* Expand a groupingSets clause to a flat list of grouping sets.
* The returned list is sorted by length, shortest sets first.
@ -1743,7 +1770,7 @@ cmp_list_len_asc(const ListCell *a, const ListCell *b)
* some consistency checks.
*/
List *
expand_grouping_sets(List *groupingSets, int limit)
expand_grouping_sets(List *groupingSets, bool groupDistinct, int limit)
{
List *expanded_groups = NIL;
List *result = NIL;
@ -1801,8 +1828,31 @@ expand_grouping_sets(List *groupingSets, int limit)
result = new_result;
}
/* Now sort the lists by length */
list_sort(result, cmp_list_len_asc);
/* Now sort the lists by length and deduplicate if necessary */
if (!groupDistinct || list_length(result) < 2)
list_sort(result, cmp_list_len_asc);
else
{
ListCell *cell;
List *prev;
/* Sort each groupset individually */
foreach(cell, result)
list_sort(lfirst(cell), list_int_cmp);
/* Now sort the list of groupsets by length and contents */
list_sort(result, cmp_list_len_contents_asc);
/* Finally, remove duplicates */
prev = list_nth_node(List, result, 0);
for_each_from(cell, result, 1)
{
if (equal(lfirst(cell), prev))
foreach_delete_current(result, cell);
else
prev = lfirst(cell);
}
}
return result;
}

2
src/backend/utils/adt/ruleutils.c
View File

@ -5517,6 +5517,8 @@ get_basic_select_query(Query *query, deparse_context *context,
appendContextKeyword(context, " GROUP BY ",
-PRETTYINDENT_STD, PRETTYINDENT_STD, 1);
if (query->groupDistinct)
appendStringInfoString(buf, "DISTINCT ");
save_exprkind = context->special_exprkind;
context->special_exprkind = EXPR_KIND_GROUP_BY;

10
src/include/nodes/parsenodes.h
View File

@ -62,6 +62,14 @@ typedef enum SortByNulls
SORTBY_NULLS_LAST
} SortByNulls;
/* Options for [ ALL | DISTINCT ] */
typedef enum SetQuantifier
{
SET_QUANTIFIER_DEFAULT,
SET_QUANTIFIER_ALL,
SET_QUANTIFIER_DISTINCT
} SetQuantifier;
/*
* Grantable rights are encoded so that we can OR them together in a bitmask.
* The present representation of AclItem limits us to 16 distinct rights,
@ -146,6 +154,7 @@ typedef struct Query
List *returningList; /* return-values list (of TargetEntry) */
List *groupClause; /* a list of SortGroupClause's */
bool groupDistinct; /* is the group by clause distinct? */
List *groupingSets; /* a list of GroupingSet's if present */
@ -1629,6 +1638,7 @@ typedef struct SelectStmt
List *fromClause; /* the FROM clause */
Node *whereClause; /* WHERE qualification */
List *groupClause; /* GROUP BY clauses */
bool groupDistinct; /* Is this GROUP BY DISTINCT? */
Node *havingClause; /* HAVING conditional-expression */
List *windowClause; /* WINDOW window_name AS (...), ... */

1
src/include/nodes/pg_list.h
View File

@ -604,6 +604,7 @@ extern pg_nodiscard List *list_copy_deep(const List *oldlist);
typedef int (*list_sort_comparator) (const ListCell *a, const ListCell *b);
extern void list_sort(List *list, list_sort_comparator cmp);
extern int list_int_cmp(const ListCell *p1, const ListCell *p2);
extern int list_oid_cmp(const ListCell *p1, const ListCell *p2);
#endif /* PG_LIST_H */

2
src/include/parser/parse_agg.h
View File

@ -26,7 +26,7 @@ extern void transformWindowFuncCall(ParseState *pstate, WindowFunc *wfunc,
extern void parseCheckAggregates(ParseState *pstate, Query *qry);
extern List *expand_grouping_sets(List *groupingSets, int limit);
extern List *expand_grouping_sets(List *groupingSets, bool groupDistinct, int limit);
extern int get_aggregate_argtypes(Aggref *aggref, Oid *inputTypes);

111
src/test/regress/expected/groupingsets.out
View File

@ -1929,4 +1929,115 @@ set work_mem to default;
drop table gs_group_1;
drop table gs_hash_1;
-- GROUP BY DISTINCT
-- "normal" behavior...
select a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by all rollup(a, b), rollup(a, c)
order by a, b, c;
a | b | c
---+---+---
1 | 2 | 3
1 | 2 |
1 | 2 |
1 | | 3
1 | | 3
1 | |
1 | |
1 | |
4 | | 6
4 | | 6
4 | | 6
4 | |
4 | |
4 | |
4 | |
4 | |
7 | 8 | 9
7 | 8 |
7 | 8 |
7 | | 9
7 | | 9
7 | |
7 | |
7 | |
| |
(25 rows)
-- ...which is also the default
select a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by rollup(a, b), rollup(a, c)
order by a, b, c;
a | b | c
---+---+---
1 | 2 | 3
1 | 2 |
1 | 2 |
1 | | 3
1 | | 3
1 | |
1 | |
1 | |
4 | | 6
4 | | 6
4 | | 6
4 | |
4 | |
4 | |
4 | |
4 | |
7 | 8 | 9
7 | 8 |
7 | 8 |
7 | | 9
7 | | 9
7 | |
7 | |
7 | |
| |
(25 rows)
-- "group by distinct" behavior...
select a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by distinct rollup(a, b), rollup(a, c)
order by a, b, c;
a | b | c
---+---+---
1 | 2 | 3
1 | 2 |
1 | | 3
1 | |
4 | | 6
4 | | 6
4 | |
4 | |
7 | 8 | 9
7 | 8 |
7 | | 9
7 | |
| |
(13 rows)
-- ...which is not the same as "select distinct"
select distinct a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by rollup(a, b), rollup(a, c)
order by a, b, c;
a | b | c
---+---+---
1 | 2 | 3
1 | 2 |
1 | | 3
1 | |
4 | | 6
4 | |
7 | 8 | 9
7 | 8 |
7 | | 9
7 | |
| |
(11 rows)
-- end

26
src/test/regress/sql/groupingsets.sql
View File

@ -529,4 +529,30 @@ set work_mem to default;
drop table gs_group_1;
drop table gs_hash_1;
-- GROUP BY DISTINCT
-- "normal" behavior...
select a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by all rollup(a, b), rollup(a, c)
order by a, b, c;
-- ...which is also the default
select a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by rollup(a, b), rollup(a, c)
order by a, b, c;
-- "group by distinct" behavior...
select a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by distinct rollup(a, b), rollup(a, c)
order by a, b, c;
-- ...which is not the same as "select distinct"
select distinct a, b, c
from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
group by rollup(a, b), rollup(a, c)
order by a, b, c;
-- end