simplify merging logic

Signed-off-by: Andres Taylor <[email protected]>

go/vt/vtgate/planbuilder/operators/join_merging.go

@@ -76,7 +76,7 @@ func mergeJoinInputs(ctx *plancontext.PlanningContext, lhs, rhs Operator, joinPr
 
 	// sharded routing is complex, so we handle it in a separate method
 	case a == sharded && b == sharded:
-		return tryMergeShardedRouting(ctx, lhsRoute, rhsRoute, m, joinPredicates, false /*isSubquery*/)
+		return tryMergeShardedRouting(ctx, lhsRoute, rhsRoute, m, joinPredicates)
 
 	default:
 		return nil

go/vt/vtgate/planbuilder/operators/sharded_routing.go

@@ -23,7 +23,6 @@ import (
 	"vitess.io/vitess/go/mysql/collations"
 	"vitess.io/vitess/go/slice"
 	"vitess.io/vitess/go/vt/sqlparser"
-	"vitess.io/vitess/go/vt/vterrors"
 	"vitess.io/vitess/go/vt/vtgate/engine"
 	"vitess.io/vitess/go/vt/vtgate/evalengine"
 	"vitess.io/vitess/go/vt/vtgate/planbuilder/plancontext"
@@ -639,9 +638,10 @@ func tryMergeShardedRouting(
 	routeA, routeB *Route,
 	m merger,
 	joinPredicates []sqlparser.Expr,
-	isSubquery bool,
 ) *Route {
-	sameKeyspace := routeA.Routing.Keyspace() == routeB.Routing.Keyspace()
+	if routeA.Routing.Keyspace() != routeB.Routing.Keyspace() {
+		return nil
+	}
 	tblA := routeA.Routing.(*ShardedRouting)
 	tblB := routeB.Routing.(*ShardedRouting)
 
@@ -670,13 +670,6 @@ func tryMergeShardedRouting(
 			return nil
 		}
 
-		if !sameKeyspace {
-			if isSubquery {
-				panic(vterrors.VT12001("cross-shard correlated subquery"))
-			}
-			return nil
-		}
-
 		canMerge := canMergeOnFilters(ctx, routeA, routeB, joinPredicates)
 		if !canMerge {
 			return nil

go/vt/vtgate/planbuilder/operators/subquery_planning.go

@@ -758,7 +758,7 @@ func mergeSubqueryInputs(ctx *plancontext.PlanningContext, in, out Operator, joi
 
 	// sharded routing is complex, so we handle it in a separate method
 	case inner == sharded && outer == sharded:
-		return tryMergeShardedRouting(ctx, inRoute, outRoute, m, joinPredicates, true /*isSubquery*/)
+		return tryMergeShardedRouting(ctx, inRoute, outRoute, m, joinPredicates)
 
 	default:
 		return nil

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

@@ -296,8 +296,8 @@
   },
   {
     "comment": "Cross keyspace query with subquery",
-    "query": "select 1 from user where id in (select id from t1)",
-    "plan": "VT12001: unsupported: cross-shard correlated subquery"
+    "query": "select 1 from user where id = (select id from t1 where user.foo = t1.bar)",
+    "plan": "VT12001: unsupported: correlated subquery is only supported for EXISTS"
   },
   {
     "comment": "multi-shard union",