backport 16384 to release-18 (vitessio#16948)

Signed-off-by: Andres Taylor <andres@planetscale.com>
Co-authored-by: vitess-bot[bot] <108069721+vitess-bot[bot]@users.noreply.github.com>

go/test/endtoend/vtgate/queries/aggregation/aggregation_test.go

@@ -390,9 +390,15 @@ func TestOrderByCount(t *testing.T) {
 	defer closer()
 
 	mcmp.Exec("insert into t9(id1, id2, id3) values(1, '1', '1'), (2, '2', '2'), (3, '2', '2'), (4, '3', '3'), (5, '3', '3'), (6, '3', '3')")
+	mcmp.Exec("insert into t1(t1_id, `name`, `value`, shardkey) values(1,'a1','foo',100), (2,'b1','foo',200), (3,'c1','foo',300), (4,'a1','foo',100), (5,'b1','bar',200)")
 
 	mcmp.Exec("SELECT t9.id2 FROM t9 GROUP BY t9.id2 ORDER BY COUNT(t9.id2) DESC")
-	mcmp.Exec("select COUNT(*) from (select 1 as one FROM t9 WHERE id3 = 3 ORDER BY id1 DESC LIMIT 3 OFFSET 0) subquery_for_count")
+	version, err := cluster.GetMajorVersion("vtgate")
+	require.NoError(t, err)
+	if version == 18 {
+		mcmp.Exec("select COUNT(*) from (select 1 as one FROM t9 WHERE id3 = 3 ORDER BY id1 DESC LIMIT 3 OFFSET 0) subquery_for_count")
+		mcmp.Exec("select t.id1, t1.name, t.leCount from (select id1, count(*) as leCount from t9 group by 1 order by 2 desc limit 20) t join t1 on t.id1 = t1.t1_id")
+	}
 }
 
 func TestAggregateAnyValue(t *testing.T) {

go/vt/vtgate/planbuilder/operators/SQL_builder.go

@@ -464,6 +464,13 @@ func buildAggregation(op *Aggregator, qb *queryBuilder) error {
 			qb.addGroupBy(weightStringFor(simplified))
 		}
 	}
+	if op.DT != nil {
+		sel := qb.asSelectStatement()
+		qb.stmt = nil
+		qb.addTableExpr(op.DT.Alias, op.DT.Alias, TableID(op), &sqlparser.DerivedTable{
+			Select: sel,
+		}, nil, op.DT.Columns)
+	}
 
 	return nil
 }

go/vt/vtgate/planbuilder/operators/horizon_expanding.go

@@ -88,7 +88,7 @@ func expandSelectHorizon(ctx *plancontext.PlanningContext, horizon *Horizon, sel
 		// if we are dealing with a derived table, we need to make sure that the ordering columns
 		// are available outside the derived table
 		for _, order := range horizon.Query.GetOrderBy() {
-			qp.addColumn(ctx, order.Expr)
+			qp.addDerivedColumn(ctx, order.Expr)
 		}
 	}
 
@@ -121,9 +121,9 @@ func expandSelectHorizon(ctx *plancontext.PlanningContext, horizon *Horizon, sel
 	}
 
 	if len(qp.OrderExprs) > 0 {
-		op = &Ordering{
-			Source: op,
-			Order:  qp.OrderExprs,
+		op, err = expandOrderBy(ctx, op, qp, horizon.Alias)
+		if err != nil {
+			return nil, nil, err
 		}
 		extracted = append(extracted, "Ordering")
 	}
@@ -139,6 +139,76 @@ func expandSelectHorizon(ctx *plancontext.PlanningContext, horizon *Horizon, sel
 	return op, rewrite.NewTree(fmt.Sprintf("expand SELECT horizon into (%s)", strings.Join(extracted, ", ")), op), nil
 }
 
+func expandOrderBy(ctx *plancontext.PlanningContext, op ops.Operator, qp *QueryProjection, derived string) (ops.Operator, error) {
+	var newOrder []ops.OrderBy
+	sqc := &SubQueryBuilder{}
+	proj, ok := op.(*Projection)
+
+	for _, expr := range qp.OrderExprs {
+		// Attempt to extract any subqueries within the expression
+		newExpr, subqs, err := sqc.pullOutValueSubqueries(ctx, expr.SimplifiedExpr, TableID(op), false)
+		if err != nil {
+			return nil, err
+		}
+		if newExpr == nil {
+			// If no subqueries are found, retain the original order expression
+			if derived != "" {
+				expr = exposeOrderingColumn(ctx, qp, expr, derived)
+			}
+			newOrder = append(newOrder, expr)
+			continue
+		}
+
+		// If the operator is not a projection, we cannot handle subqueries with aggregation
+		if !ok {
+			return nil, vterrors.VT12001("subquery with aggregation in order by")
+		}
+
+		// Add the new subquery expression to the projection
+		if err := proj.addSubqueryExpr(aeWrap(newExpr), newExpr, subqs...); err != nil {
+			return nil, err
+		}
+		// Replace the original order expression with the new expression containing subqueries
+		newOrder = append(newOrder, ops.OrderBy{
+			Inner: &sqlparser.Order{
+				Expr:      newExpr,
+				Direction: expr.Inner.Direction,
+			},
+			SimplifiedExpr: newExpr,
+		})
+	}
+
+	// Update the source of the projection if we have it
+	if proj != nil {
+		proj.Source = sqc.getRootOperator(proj.Source)
+	}
+
+	// Return the updated operator with the new order by expressions
+	return &Ordering{
+		Source: op,
+		Order:  newOrder,
+	}, nil
+}
+
+// exposeOrderingColumn will expose the ordering column to the outer query
+func exposeOrderingColumn(ctx *plancontext.PlanningContext, qp *QueryProjection, orderBy ops.OrderBy, derived string) ops.OrderBy {
+	for _, se := range qp.SelectExprs {
+		aliasedExpr, err := se.GetAliasedExpr()
+		if err != nil {
+			panic(vterrors.VT13001("unexpected expression in select"))
+		}
+		if ctx.SemTable.EqualsExprWithDeps(aliasedExpr.Expr, orderBy.SimplifiedExpr) {
+			newExpr := sqlparser.NewColNameWithQualifier(aliasedExpr.ColumnName(), sqlparser.NewTableName(derived))
+			ctx.SemTable.CopySemanticInfo(orderBy.SimplifiedExpr, newExpr)
+			orderBy.SimplifiedExpr = newExpr
+			orderBy.Inner = &sqlparser.Order{Expr: newExpr, Direction: orderBy.Inner.Direction}
+			break
+		}
+	}
+
+	return orderBy
+}
+
 func createProjectionFromSelect(ctx *plancontext.PlanningContext, horizon *Horizon) (out ops.Operator, err error) {
 	qp, err := horizon.getQP(ctx)
 	if err != nil {

go/vt/vtgate/planbuilder/operators/queryprojection.go

@@ -807,8 +807,9 @@ func (qp *QueryProjection) useGroupingOverDistinct(ctx *plancontext.PlanningCont
 	return true, nil
 }
 
-// addColumn adds a column to the QueryProjection if it is not already present
-func (qp *QueryProjection) addColumn(ctx *plancontext.PlanningContext, expr sqlparser.Expr) {
+// addColumn adds a column to the QueryProjection if it is not already present.
+// It will use a column name that is available on the outside of the derived table
+func (qp *QueryProjection) addDerivedColumn(ctx *plancontext.PlanningContext, expr sqlparser.Expr) {
 	for _, selectExpr := range qp.SelectExprs {
 		getExpr, err := selectExpr.GetExpr()
 		if err != nil {

go/vt/vtgate/planbuilder/testdata/aggr_cases.json

@@ -716,6 +716,58 @@
       ]
     }
   },
+  {
+    "comment": "Aggregation with derived table",
+    "query": "select u.id, u.name, t.num_segments from (select id, count(*) as num_segments from user group by 1 order by 2 desc limit 20) t join unsharded u on u.id = t.id",
+    "plan": {
+      "QueryType": "SELECT",
+      "Original": "select u.id, u.name, t.num_segments from (select id, count(*) as num_segments from user group by 1 order by 2 desc limit 20) t join unsharded u on u.id = t.id",
+      "Instructions": {
+        "OperatorType": "Join",
+        "Variant": "Join",
+        "JoinColumnIndexes": "R:0,R:1,L:0",
+        "JoinVars": {
+          "t_id": 1
+        },
+        "TableName": "`user`_unsharded",
+        "Inputs": [
+          {
+            "OperatorType": "Limit",
+            "Count": "INT64(20)",
+            "Inputs": [
+              {
+                "OperatorType": "Route",
+                "Variant": "Scatter",
+                "Keyspace": {
+                  "Name": "user",
+                  "Sharded": true
+                },
+                "FieldQuery": "select t.num_segments, t.id from (select id, count(*) as num_segments from `user` where 1 != 1 group by id) as t where 1 != 1",
+                "OrderBy": "0 DESC",
+                "Query": "select t.num_segments, t.id from (select id, count(*) as num_segments from `user` group by id) as t order by t.num_segments desc limit :__upper_limit",
+                "Table": "`user`"
+              }
+            ]
+          },
+          {
+            "OperatorType": "Route",
+            "Variant": "Unsharded",
+            "Keyspace": {
+              "Name": "main",
+              "Sharded": false
+            },
+            "FieldQuery": "select u.id, u.`name` from unsharded as u where 1 != 1",
+            "Query": "select u.id, u.`name` from unsharded as u where u.id = :t_id",
+            "Table": "unsharded"
+          }
+        ]
+      },
+      "TablesUsed": [
+        "main.unsharded",
+        "user.user"
+      ]
+    }
+  },
   {
     "comment": "scatter aggregate multiple group by (numbers)",
     "query": "select a, b, count(*) from user group by 2, 1",
@@ -3540,7 +3592,7 @@
                     },
                     "FieldQuery": "select id, val1, 1, weight_string(val1) from (select id, val1 from `user` where 1 != 1) as x where 1 != 1",
                     "OrderBy": "(1|3) ASC",
-                    "Query": "select id, val1, 1, weight_string(val1) from (select id, val1 from `user` where val2 < 4) as x order by `user`.val1 asc limit :__upper_limit",
+                    "Query": "select id, val1, 1, weight_string(val1) from (select id, val1 from `user` where val2 < 4) as x order by x.val1 asc limit :__upper_limit",
                     "Table": "`user`"
                   }
                 ]
@@ -6439,7 +6491,7 @@
                 },
                 "FieldQuery": "select 1, id, weight_string(id) from (select 1 as one, id from `user` where 1 != 1) as subquery_for_count where 1 != 1",
                 "OrderBy": "(1|2) DESC",
-                "Query": "select 1, id, weight_string(id) from (select 1 as one, id from `user` where `user`.is_not_deleted = true) as subquery_for_count order by id desc limit :__upper_limit",
+                "Query": "select 1, id, weight_string(id) from (select 1 as one, id from `user` where `user`.is_not_deleted = true) as subquery_for_count order by subquery_for_count.id desc limit :__upper_limit",
                 "Table": "`user`"
               }
             ]
@@ -6455,5 +6507,43 @@
     "comment": "baz in the HAVING clause can't be accessed because of the GROUP BY",
     "query": "select foo, count(bar) as x from user group by foo having baz > avg(baz) order by x",
     "plan": "Unknown column 'baz' in 'having clause'"
+  },
+  {
+    "comment": "Aggregation over a ORDER BY/LIMIT inside a derived table",
+    "query": "SELECT COUNT(*) FROM (SELECT 1 AS one FROM `user` WHERE `user`.`is_not_deleted` = true ORDER BY id DESC LIMIT 25 OFFSET 0) subquery_for_count",
+    "plan": {
+      "QueryType": "SELECT",
+      "Original": "SELECT COUNT(*) FROM (SELECT 1 AS one FROM `user` WHERE `user`.`is_not_deleted` = true ORDER BY id DESC LIMIT 25 OFFSET 0) subquery_for_count",
+      "Instructions": {
+        "OperatorType": "Aggregate",
+        "Variant": "Scalar",
+        "Aggregates": "count_star(0) AS count(*)",
+        "ResultColumns": 1,
+        "Inputs": [
+          {
+            "OperatorType": "Limit",
+            "Count": "INT64(25)",
+            "Offset": "INT64(0)",
+            "Inputs": [
+              {
+                "OperatorType": "Route",
+                "Variant": "Scatter",
+                "Keyspace": {
+                  "Name": "user",
+                  "Sharded": true
+                },
+                "FieldQuery": "select 1, id, weight_string(id) from (select 1 as one, id from `user` where 1 != 1) as subquery_for_count where 1 != 1",
+                "OrderBy": "(1|2) DESC",
+                "Query": "select 1, id, weight_string(id) from (select 1 as one, id from `user` where `user`.is_not_deleted = true) as subquery_for_count order by subquery_for_count.id desc limit :__upper_limit",
+                "Table": "`user`"
+              }
+            ]
+          }
+        ]
+      },
+      "TablesUsed": [
+        "user.user"
+      ]
+    }
   }
 ]