planner: fix panic when building index merge plan (#23141)

planner/core/integration_test.go

@@ -2607,6 +2607,22 @@ func (s *testIntegrationSuite) TestReorderSimplifiedOuterJoins(c *C) {
 	}
 }
 
+func (s *testIntegrationSuite) TestIndexMergeConstantTrue(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("create table t(a int primary key, b int not null, key(b))")
+	tk.MustExec("delete /*+ use_index_merge(t) */ FROM t WHERE a=1 OR (b < SOME (SELECT /*+ use_index_merge(t)*/ b FROM t WHERE a<2 OR b<2))")
+
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int not null, b int not null, key(a), key(b))")
+	tk.MustExec("delete /*+ use_index_merge(t) */ FROM t WHERE a=1 OR (b < SOME (SELECT /*+ use_index_merge(t)*/ b FROM t WHERE a<2 OR b<2))")
+
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int primary key, b int not null, c int, key(a), key(b,c))")
+	tk.MustExec("delete /*+ use_index_merge(t) */ FROM t WHERE a=1 OR (a<2 and b<2)")
+}
+
 func (s *testIntegrationSerialSuite) TestPushDownAggForMPP(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")

planner/core/stats.go

@@ -506,8 +506,10 @@ func (ds *DataSource) accessPathsForConds(conditions []expression.Expression, us
 				logutil.BgLogger().Debug("can not derive statistics of a path", zap.Error(err))
 				continue
 			}
-			if len(path.AccessConds) == 0 {
-				// If AccessConds is empty, we ignore the access path.
+			// If `AccessConds` is empty, we ignore the access path.
+			// If the path contains a full range, ignore it also. This can happen when `AccessConds` is constant true, and
+			// it comes from the result of a subquery, so it is not folded.
+			if len(path.AccessConds) == 0 || ranger.HasFullRange(path.Ranges) {
 				continue
 			}
 			// If we have point or empty range, just remove other possible paths.
@@ -531,8 +533,10 @@ func (ds *DataSource) accessPathsForConds(conditions []expression.Expression, us
 				continue
 			}
 			noIntervalRanges := ds.deriveIndexPathStats(path, conditions, true)
-			if len(path.AccessConds) == 0 {
-				// If AccessConds is empty, we ignore the access path.
+			// If `AccessConds` is empty, we ignore the access path.
+			// If the path contains a full range, ignore it also. This can happen when `AccessConds` is constant true, and
+			// it comes from the result of a subquery, so it is not folded.
+			if len(path.AccessConds) == 0 || ranger.HasFullRange(path.Ranges) {
 				continue
 			}
 			// If we have empty range, or point range on unique index, just remove other possible paths.
@@ -561,9 +565,9 @@ func (ds *DataSource) buildIndexMergePartialPath(indexAccessPaths []*util.Access
 	minEstRowIndex := 0
 	minEstRow := math.MaxFloat64
 	for i := 0; i < len(indexAccessPaths); i++ {
-		rc, err := ds.stats.HistColl.GetRowCountByIndexRanges(ds.ctx.GetSessionVars().StmtCtx, indexAccessPaths[i].Index.ID, indexAccessPaths[i].Ranges)
-		if err != nil {
-			return nil, err
+		rc := indexAccessPaths[i].CountAfterAccess
+		if len(indexAccessPaths[i].IndexFilters) > 0 {
+			rc = indexAccessPaths[i].CountAfterIndex
 		}
 		if rc < minEstRow {
 			minEstRowIndex = i

util/ranger/types.go

@@ -122,6 +122,16 @@ func (ran *Range) IsFullRange() bool {
 	return true
 }
 
+// HasFullRange checks if any range in the slice is a full range.
+func HasFullRange(ranges []*Range) bool {
+	for _, ran := range ranges {
+		if ran.IsFullRange() {
+			return true
+		}
+	}
+	return false
+}
+
 // String implements the Stringer interface.
 func (ran *Range) String() string {
 	lowStrs := make([]string, 0, len(ran.LowVal))