planner: fix the issue that MVIndex leads to "can't find plan" error (#…

…52067)

close #49438

pkg/planner/core/casetest/BUILD.bazel

@@ -12,7 +12,7 @@ go_test(
     ],
     data = glob(["testdata/**"]),
     flaky = True,
-    shard_count = 21,
+    shard_count = 22,
     deps = [
         "//pkg/domain",
         "//pkg/parser",

pkg/planner/core/casetest/integration_test.go

@@ -421,6 +421,15 @@ func TestFixControl45132(t *testing.T) {
 	tk.MustHavePlan(`select * from t where a=2`, `TableFullScan`)
 }
 
+func TestIssue49438(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec(`use test`)
+	tk.MustExec(`drop table if exists tx`)
+	tk.MustExec(`create table tx (a int, b json, key k(a, (cast(b as date array))))`)
+	tk.MustExec(`select 1 from tx where a in (1)`) // no error
+}
+
 func TestIssue52023(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 

pkg/planner/core/find_best_task.go

@@ -748,6 +748,12 @@ func compareIndexBack(lhs, rhs *candidatePath) (int, bool) {
 // compareCandidates is the core of skyline pruning, which is used to decide which candidate path is better.
 // The return value is 1 if lhs is better, -1 if rhs is better, 0 if they are equivalent or not comparable.
 func compareCandidates(sctx PlanContext, prop *property.PhysicalProperty, lhs, rhs *candidatePath) int {
+	// Due to #50125, full scan on MVIndex has been disabled, so MVIndex path might lead to 'can't find a proper plan' error at the end.
+	// Avoid MVIndex path to exclude all other paths and leading to 'can't find a proper plan' error, see #49438 for an example.
+	if isMVIndexPath(lhs.path) || isMVIndexPath(rhs.path) {
+		return 0
+	}
+
 	// This rule is empirical but not always correct.
 	// If x's range row count is significantly lower than y's, for example, 1000 times, we think x is better.
 	if lhs.path.CountAfterAccess > 100 && rhs.path.CountAfterAccess > 100 && // to prevent some extreme cases, e.g. 0.01 : 10