fix: derived table join column expression to be part of add join predicate on rewrite

go/test/endtoend/vtgate/queries/derived/derived_test.go

@@ -113,3 +113,15 @@ func TestDerivedTablesWithLimit(t *testing.T) {
                 (SELECT id, user_id FROM music LIMIT 10) as m on u.id = m.user_id`,
 		`[[INT64(1) INT64(1)] [INT64(5) INT64(2)] [INT64(1) INT64(3)] [INT64(2) INT64(4)] [INT64(3) INT64(5)] [INT64(5) INT64(7)] [INT64(4) INT64(6)] [INT64(6) NULL]]`)
 }
+
+// TestDerivedTableColumnAliasWithJoin tests the derived table having alias column and using it in the join condition
+func TestDerivedTableColumnAliasWithJoin(t *testing.T) {
+	utils.SkipIfBinaryIsBelowVersion(t, 20, "vtgate")
+	mcmp, closer := start(t)
+	defer closer()
+
+	mcmp.Exec(`SELECT user.id FROM user join (SELECT id as uid FROM user) t on t.uid = user.id`)
+	mcmp.Exec(`SELECT user.id FROM user left join (SELECT id as uid FROM user) t on t.uid = user.id`)
+	mcmp.Exec(`SELECT user.id FROM user join (SELECT id FROM user) t(uid) on t.uid = user.id`)
+	mcmp.Exec(`SELECT user.id FROM user left join (SELECT id FROM user) t(uid) on t.uid = user.id`)
+}

go/vt/vtgate/planbuilder/operators/horizon.go

@@ -99,7 +99,7 @@ func (h *Horizon) AddPredicate(ctx *plancontext.PlanningContext, expr sqlparser.
 		panic(err)
 	}
 
-	newExpr := semantics.RewriteDerivedTableExpression(expr, tableInfo)
+	newExpr := ctx.RewriteDerivedTableExpression(expr, tableInfo)
 	if ContainsAggr(ctx, newExpr) {
 		return newFilter(h, expr)
 	}

go/vt/vtgate/planbuilder/operators/rewriters.go

@@ -218,6 +218,9 @@ func bottomUp(
 			childID = childID.Merge(resolveID(oldInputs[0]))
 		}
 		in, changed := bottomUp(operator, childID, resolveID, rewriter, shouldVisit, false)
+		if DebugOperatorTree && changed.Changed() {
+			fmt.Println(ToTree(in))
+		}
 		anythingChanged = anythingChanged.Merge(changed)
 		newInputs[i] = in
 	}

go/vt/vtgate/planbuilder/plancontext/planning_context.go

@@ -188,3 +188,16 @@ func (ctx *PlanningContext) execOnJoinPredicateEqual(joinPred sqlparser.Expr, fn
 	}
 	return false
 }
+
+func (ctx *PlanningContext) RewriteDerivedTableExpression(expr sqlparser.Expr, tableInfo semantics.TableInfo) sqlparser.Expr {
+	modifiedExpr := semantics.RewriteDerivedTableExpression(expr, tableInfo)
+	for key, exprs := range ctx.joinPredicates {
+		for _, rhsExpr := range exprs {
+			if ctx.SemTable.EqualsExpr(expr, rhsExpr) {
+				ctx.joinPredicates[key] = append(ctx.joinPredicates[key], modifiedExpr)
+				return modifiedExpr
+			}
+		}
+	}
+	return modifiedExpr
+}

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

@@ -5221,5 +5221,27 @@
         "main.unsharded_a"
       ]
     }
+  },
+  {
+    "comment": "join with derived table with alias and join condition - merge into route",
+    "query": "select 1 from user join (select id as uid from user) as t where t.uid = user.id",
+    "plan": {
+      "QueryType": "SELECT",
+      "Original": "select 1 from user join (select id as uid from user) as t where t.uid = user.id",
+      "Instructions": {
+        "OperatorType": "Route",
+        "Variant": "Scatter",
+        "Keyspace": {
+          "Name": "user",
+          "Sharded": true
+        },
+        "FieldQuery": "select 1 from (select id as uid from `user` where 1 != 1) as t, `user` where 1 != 1",
+        "Query": "select 1 from (select id as uid from `user`) as t, `user` where t.uid = `user`.id",
+        "Table": "`user`"
+      },
+      "TablesUsed": [
+        "user.user"
+      ]
+    }
   }
 ]