cardinality: remove the unnecessary limitation that the "exponential backoff" entry stats can't use iteself for estimation (#56850)

close pingcap/tidb#56915

pkg/planner/cardinality/row_count_index.go

@@ -476,9 +476,6 @@ func expBackoffEstimation(sctx planctx.PlanContext, idx *statistics.Index, coll
 			// `GetRowCountByIndexRanges()` when the input `indexRange` is a multi-column range. This
 			// check avoids infinite recursion.
 			for _, idxID := range idxIDs {
-				if idxID == idx.Histogram.ID {
-					continue
-				}
 				idxStats := coll.GetIdx(idxID)
 				if idxStats == nil || statistics.IndexStatsIsInvalid(sctx, idxStats, coll, idxID) {
 					continue

pkg/planner/core/casetest/BUILD.bazel

@@ -12,7 +12,7 @@ go_test(
     ],
     data = glob(["testdata/**"]),
     flaky = True,
-    shard_count = 27,
+    shard_count = 28,
     deps = [
         "//pkg/domain",
         "//pkg/errno",

pkg/planner/core/casetest/integration_test.go

@@ -515,3 +515,22 @@ func TestIndexMergeJSONMemberOf2FlakyPart(t *testing.T) {
 		"└─TableRowIDScan_6(Probe) 1.00 cop[tikv] table:t keep order:false, stats:partial[d:unInitialized]",
 	))
 }
+
+func TestIssue56915(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec(`use test`)
+	tk.MustExec(`drop table if exists t`)
+	tk.MustExec(`create table t(a int, b int, j json, index ia(a), index mvi( (cast(j as signed array)), a, b) );`)
+	tk.MustExec(`insert into t value(1,1,'[1,2,3,4,5]');`)
+	tk.MustExec(`insert into t value(1,1,'[1,2,3,4,5]');`)
+	tk.MustExec(`insert into t value(1,1,'[1,2,3,4,5]');`)
+	tk.MustExec(`insert into t value(1,1,'[1,2,3,4,5]');`)
+	tk.MustExec(`insert into t value(1,1,'[6]');`)
+	tk.MustExec(`analyze table t all columns;`)
+	tk.MustQuery("explain format = brief select * from t where a = 1 and 6 member of (j);").Check(testkit.Rows(
+		"IndexMerge 1.00 root  type: union",
+		"├─IndexRangeScan(Build) 1.00 cop[tikv] table:t, index:mvi(cast(`j` as signed array), a, b) range:[6 1,6 1], keep order:false, stats:partial[j:unInitialized]",
+		"└─TableRowIDScan(Probe) 1.00 cop[tikv] table:t keep order:false, stats:partial[j:unInitialized]",
+	))
+}

tests/integrationtest/t/planner/core/indexmerge_path.test

@@ -15,7 +15,6 @@ analyze table t index a;
 analyze table t index a, idx, idx2;
 --disable_warnings
 
-
 # TestIndexMergeJSONMemberOf
 drop table if exists t;
 create table t(
@@ -503,4 +502,3 @@ EXPLAIN format = brief SELECT /*+ use_index_merge(t1, mvi4) */ * from t1 where
 c = 1 and
 json_contains(j, '[4,5]') and
 d not like '%test%';
-