Fix aliasing in routes that have a derived table (#15550)

Signed-off-by: Manan Gupta <manan@planetscale.com>

go/test/endtoend/vtgate/queries/reference/reference_test.go

@@ -83,6 +83,25 @@ func TestReferenceRouting(t *testing.T) {
 		`[[INT64(0)]]`,
 	)
 
+	t.Run("Complex reference query", func(t *testing.T) {
+		utils.SkipIfBinaryIsBelowVersion(t, 20, "vtgate")
+		// Verify a complex query using reference tables with a left join having a derived table with an order by clause works as intended.
+		utils.AssertMatches(
+			t,
+			conn,
+			`SELECT t.id FROM (
+                        SELECT zd.id, zd.zip_id
+                        FROM `+shardedKeyspaceName+`.zip_detail AS zd
+                        WHERE zd.id IN (2)
+                        ORDER BY zd.discontinued_at
+                        LIMIT 1
+                ) AS t
+                LEFT JOIN `+shardedKeyspaceName+`.zip_detail AS t0 ON t.zip_id = t0.zip_id
+                ORDER BY t.id`,
+			`[[INT64(2)]]`,
+		)
+	})
+
 	// UPDATE should route an unqualified zip_detail to unsharded keyspace.
 	utils.Exec(t, conn,
 		"UPDATE zip_detail SET discontinued_at = NULL WHERE id = 2")

go/vt/vtgate/planbuilder/operators/route.go

@@ -656,6 +656,11 @@ func addMultipleColumnsToInput(
 		}
 		return derivedName, op, added, offset
 
+	case *Horizon:
+		// if the horizon has an alias, then it is a derived table,
+		// we have to add a new projection and can't build on this one
+		return op.Alias, op, false, nil
+
 	case selectExpressions:
 		name := op.derivedName()
 		if name != "" {

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

@@ -6249,8 +6249,8 @@
               "Name": "user",
               "Sharded": true
             },
-            "FieldQuery": "select table_name from (select table_name from `user` where 1 != 1 group by table_name) as `tables` where 1 != 1",
-            "Query": "select table_name from (select table_name from `user` where id = 143 group by table_name) as `tables`",
+            "FieldQuery": "select `tables`.table_name from (select table_name from `user` where 1 != 1 group by table_name) as `tables` where 1 != 1",
+            "Query": "select `tables`.table_name from (select table_name from `user` where id = 143 group by table_name) as `tables`",
             "Table": "`user`",
             "Values": [
               "143"

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

@@ -4216,8 +4216,8 @@
                   "Name": "user",
                   "Sharded": true
                 },
-                "FieldQuery": "select id, col from (select id, col from `user` where 1 != 1) as u where 1 != 1",
-                "Query": "select distinct id, col from (select id, col from `user`) as u",
+                "FieldQuery": "select u.id, u.col from (select id, col from `user` where 1 != 1) as u where 1 != 1",
+                "Query": "select distinct u.id, u.col from (select id, col from `user`) as u",
                 "Table": "`user`"
               },
               {

go/vt/vtgate/planbuilder/testdata/info_schema57_cases.json

@@ -1162,8 +1162,8 @@
               "Name": "main",
               "Sharded": false
             },
-            "FieldQuery": "select table_name from (select table_name from information_schema.`tables` where 1 != 1) as `tables` where 1 != 1",
-            "Query": "select table_name from (select table_name from information_schema.`tables` where table_schema != 'information_schema' limit 1) as `tables`",
+            "FieldQuery": "select `tables`.table_name from (select table_name from information_schema.`tables` where 1 != 1) as `tables` where 1 != 1",
+            "Query": "select `tables`.table_name from (select table_name from information_schema.`tables` where table_schema != 'information_schema' limit 1) as `tables`",
             "Table": "information_schema.`tables`"
           },
           {

go/vt/vtgate/planbuilder/testdata/info_schema80_cases.json

@@ -1284,8 +1284,8 @@
               "Name": "main",
               "Sharded": false
             },
-            "FieldQuery": "select table_name from (select table_name from information_schema.`tables` where 1 != 1) as `tables` where 1 != 1",
-            "Query": "select table_name from (select table_name from information_schema.`tables` where table_schema != 'information_schema' limit 1) as `tables`",
+            "FieldQuery": "select `tables`.table_name from (select table_name from information_schema.`tables` where 1 != 1) as `tables` where 1 != 1",
+            "Query": "select `tables`.table_name from (select table_name from information_schema.`tables` where table_schema != 'information_schema' limit 1) as `tables`",
             "Table": "information_schema.`tables`"
           },
           {

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

@@ -161,6 +161,50 @@
       ]
     }
   },
+  {
+    "comment": "Reference tables using left join with a derived table having a limit clause",
+    "query": "SELECT u.id FROM ( SELECT a.id, a.u_id FROM user.ref_with_source AS a WHERE a.id IN (3) ORDER BY a.d_at LIMIT 1) as u LEFT JOIN user.ref_with_source AS u0 ON u.u_id = u0.u_uid ORDER BY u.id",
+    "plan": {
+      "QueryType": "SELECT",
+      "Original": "SELECT u.id FROM ( SELECT a.id, a.u_id FROM user.ref_with_source AS a WHERE a.id IN (3) ORDER BY a.d_at LIMIT 1) as u LEFT JOIN user.ref_with_source AS u0 ON u.u_id = u0.u_uid ORDER BY u.id",
+      "Instructions": {
+        "OperatorType": "Join",
+        "Variant": "LeftJoin",
+        "JoinColumnIndexes": "L:0",
+        "JoinVars": {
+          "u_u_id": 1
+        },
+        "TableName": "ref_with_source_ref_with_source",
+        "Inputs": [
+          {
+            "OperatorType": "Route",
+            "Variant": "Reference",
+            "Keyspace": {
+              "Name": "user",
+              "Sharded": true
+            },
+            "FieldQuery": "select u.id, u.u_id from (select a.id, a.u_id from ref_with_source as a where 1 != 1) as u where 1 != 1",
+            "Query": "select u.id, u.u_id from (select a.id, a.u_id from ref_with_source as a where a.id in (3) order by a.d_at asc limit 1) as u order by u.id asc",
+            "Table": "ref_with_source"
+          },
+          {
+            "OperatorType": "Route",
+            "Variant": "Reference",
+            "Keyspace": {
+              "Name": "user",
+              "Sharded": true
+            },
+            "FieldQuery": "select 1 from ref_with_source as u0 where 1 != 1",
+            "Query": "select 1 from ref_with_source as u0 where u0.u_uid = :u_u_id",
+            "Table": "ref_with_source"
+          }
+        ]
+      },
+      "TablesUsed": [
+        "user.ref_with_source"
+      ]
+    }
+  },
   {
     "comment": "insert into qualified ambiguous reference table routes to source",
     "query": "insert into user.ambiguous_ref_with_source(col) values(1)",

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

@@ -5043,8 +5043,8 @@
               "Name": "main",
               "Sharded": false
             },
-            "FieldQuery": "select table_name from (select table_name from unsharded where 1 != 1) as `tables` where 1 != 1",
-            "Query": "select table_name from (select table_name from unsharded limit 1) as `tables`",
+            "FieldQuery": "select `tables`.table_name from (select table_name from unsharded where 1 != 1) as `tables` where 1 != 1",
+            "Query": "select `tables`.table_name from (select table_name from unsharded limit 1) as `tables`",
             "Table": "unsharded"
           },
           {