optbuilder: allow non-aggregate expressions when GROUP BY cols are un…

…ique

This extends support for queries such as this pseudo-SQL:
```
SELECT * FROM t1 GROUP BY pk_cols;
```
To also support:
```
SELECT * FROM t1 GROUP BY unique_index_non_nullable_key_cols;
SELECT * FROM t1 GROUP BY unique_without_index_non_nullable_key_cols;
```
All unique index or unique constraint columns must be not nullable for
the query to not error out.

Fixes: #99444

Release note (sql change): This patch adds support for non-aggregate
expressions involving columns outside of the grouping columns when the
grouping columns include all key columns of a unique index and those key
columns are not nullable.

pkg/ccl/logictestccl/testdata/logic_test/regional_by_row_query_behavior

@@ -3445,3 +3445,42 @@ distribute
       │    └── filters
       │         └── t1.b = regional_by_row_table_virt_partial.pk
       └── 1
+
+subtest groupByUnique
+
+# GROUP BY unique column v doesn't allow non-aggregate expressions in the
+# SELECT list because v is not marked as NOT NULL.
+statement error pq: column "pk" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT pk, a, b FROM regional_by_row_table_virt GROUP BY v;
+
+statement ok
+ALTER TABLE regional_by_row_table_virt ALTER COLUMN v SET NOT NULL
+
+# GROUP BY unique column v allows non-aggregate expressions in the
+# SELECT list because v is marked as NOT NULL.
+query III
+SELECT pk, a, b FROM regional_by_row_table_virt GROUP BY v;
+----
+1  1  1
+
+# GROUP BY unique index column "a" doesn't allow non-aggregate expressions in
+# the SELECT list because "a" is not marked as NOT NULL.
+statement error pq: column "pk" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT pk FROM regional_by_row_table_virt GROUP BY a;
+
+statement ok
+ALTER TABLE regional_by_row_table_virt ALTER COLUMN v SET NOT NULL
+
+# GROUP BY unique index column a allows non-aggregate expressions in the
+# SELECT list because v is marked as NOT NULL.
+query I
+SELECT pk FROM regional_by_row_table_virt GROUP BY v;
+----
+1
+
+# GROUP BY unique expression index (a+10) doesn't currently allow non-aggregate
+# expressions in the SELECT list. This could potentially be supported in the
+# future. The index need not be an expression index if the GROUP BY expression
+# can be proven to be monotonically increasing or decreasing.
+statement error pq: column "pk" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT pk FROM regional_by_row_table_virt GROUP BY (a+10);

pkg/sql/logictest/testdata/logic_test/unique

@@ -872,3 +872,79 @@ SELECT * FROM uniq_fk_child
 a  b     c  d     e
 1  1     1  1     1
 2  NULL  2  NULL  NULL
+
+subtest GroupByUnique
+
+# Group by UNIQUE WITHOUT INDEX columns which are nullable must not allow
+# non-aggregate expressions outside of the grouping columns.
+statement error pq: column "b" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT b FROM uniq_hidden_pk GROUP BY a
+
+# Group by UNIQUE INDEX columns which are nullable must not allow non-aggregate
+# expressions outside of the grouping columns.
+statement error pq: column "x" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT x FROM uniq GROUP BY v
+
+# Group by UNIQUE WITHOUT INDEX constraint can allow non-aggregate expressions
+# outside of the grouping columns if the constraint is not null.
+query TI colnames,rowsort
+SELECT r, i FROM uniq_enum GROUP BY i
+----
+r        i
+us-west  1
+eu-west  2
+
+statement ok
+ALTER TABLE uniq_hidden_pk ALTER COLUMN b SET NOT NULL
+
+# Group by UNIQUE WITHOUT INDEX constraint cannot allow non-aggregate
+# expressions if any of index columns is nullable.
+statement error pq: column "a" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT a FROM uniq_hidden_pk GROUP BY b, c
+
+statement ok
+ALTER TABLE uniq_hidden_pk ALTER COLUMN c SET NOT NULL
+
+# Group by UNIQUE WITHOUT INDEX constraint can allow non-aggregate expressions
+# outside of the grouping columns if the constraint is not nullable.
+query II colnames,rowsort
+SELECT a,d FROM uniq_hidden_pk GROUP BY b, c
+----
+a  d
+1  1
+2  2
+
+# Group by a subset of UNIQUE WITHOUT INDEX columns must not allow non-aggregate
+# expressions outside of the grouping columns.
+statement error pq: column "a" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT a FROM uniq_hidden_pk GROUP BY b
+
+# Group by UNIQUE INDEX constraint cannot allow non-aggregate expressions
+# outside of the grouping columns if index columns are nullable.
+statement error pq: column "x" must appear in the GROUP BY clause or be used in an aggregate function
+SELECT x FROM uniq GROUP BY v
+
+statement ok
+ALTER TABLE uniq ALTER COLUMN v SET NOT NULL
+
+# Group by UNIQUE INDEX constraint can allow non-aggregate expressions
+# outside of the grouping columns if index columns are not nullable.
+query I colnames,rowsort
+SELECT x FROM uniq GROUP BY v ORDER BY v
+----
+x
+1
+2
+3
+NULL
+5
+NULL
+2
+NULL
+1
+NULL
+NULL
+20
+NULL
+NULL
+NULL

pkg/sql/opt/optbuilder/groupby.go

@@ -924,9 +924,12 @@ func newGroupingError(name tree.Name) error {
 }
 
 // allowImplicitGroupingColumn returns true if col is part of a table and the
-// the groupby metadata indicates that we are grouping on the entire PK of that
-// table. In that case, we can allow col as an "implicit" grouping column, even
-// if it is not specified in the query.
+// groupby metadata indicates that we are grouping on the entire PK, an entire
+// unique index key, or an entire unique without index key of that table. In
+// that case, we can allow col as an "implicit" grouping column, even if it is
+// not specified in the query.
+// In the unique index or unique without index cases, all key columns must be
+// marked as NOT NULL to allow the implicit grouping.
 func (b *Builder) allowImplicitGroupingColumn(colID opt.ColumnID, g *groupby) bool {
 	md := b.factory.Metadata()
 	colMeta := md.ColumnMeta(colID)
@@ -935,6 +938,7 @@ func (b *Builder) allowImplicitGroupingColumn(colID opt.ColumnID, g *groupby) bo
 	}
 	// Get all the PK columns.
 	tab := md.Table(colMeta.Table)
+	tabMeta := md.TableMeta(colMeta.Table)
 	var pkCols opt.ColSet
 	if tab.IndexCount() == 0 {
 		// Virtual tables have no indexes.
@@ -949,5 +953,51 @@ func (b *Builder) allowImplicitGroupingColumn(colID opt.ColumnID, g *groupby) bo
 	for i := range groupingCols {
 		pkCols.Remove(groupingCols[i].id)
 	}
-	return pkCols.Empty()
+	if pkCols.Empty() {
+		return true
+	}
+	// Check UNIQUE WITHOUT INDEX constraints.
+	for i := 0; i < tab.UniqueCount(); i++ {
+		uniqueConstraint := tab.Unique(i)
+		var uniqueCols opt.ColSet
+		nullable := false
+		for j := 0; j < uniqueConstraint.ColumnCount(); j++ {
+			column := tab.Column(uniqueConstraint.ColumnOrdinal(tab, j))
+			if column.IsNullable() {
+				nullable = true
+			}
+			columnID := tabMeta.MetaID.ColumnID(uniqueConstraint.ColumnOrdinal(tab, j))
+			uniqueCols.Add(columnID)
+		}
+		if nullable {
+			// There may be duplicate rows with nulls in unique constraint columns, so
+			// we cannot treat the constraint as truly unique if any of its columns is
+			// nullable.
+			continue
+		}
+		for k := range groupingCols {
+			uniqueCols.Remove(groupingCols[k].id)
+		}
+		if uniqueCols.Empty() {
+			return true
+		}
+	}
+	// Check UNIQUE INDEX constraints.
+	for i := 1; i < tab.IndexCount(); i++ {
+		index := tab.Index(i)
+		if !index.IsUnique() || index.IsInverted() {
+			continue
+		}
+		// If any of the key columns is nullable, uniqueCols is suffixed with the
+		// primary key columns, so we don't have to explicitly check for nullable
+		// columns here.
+		uniqueCols := tabMeta.IndexKeyColumns(i)
+		for j := range groupingCols {
+			uniqueCols.Remove(groupingCols[j].id)
+		}
+		if uniqueCols.Empty() {
+			return true
+		}
+	}
+	return false
 }