planner: let the planner can select IndexMerge on MVIndex without hint (

#40347)

ref #40191

planner/core/indexmerge_path.go

@@ -515,10 +515,6 @@ func (ds *DataSource) generateIndexMergeJSONMVIndexPath(normalPathCnt int, filte
 		if ds.possibleAccessPaths[idx].IsTablePath() || ds.possibleAccessPaths[idx].Index == nil || !ds.possibleAccessPaths[idx].Index.MVIndex {
 			continue // not a MVIndex path
 		}
-		if !ds.isSpecifiedInIndexMergeHints(ds.possibleAccessPaths[idx].Index.Name.L) {
-			continue // for safety, only consider using MVIndex when there is a `use_index_merge` hint now.
-			// TODO: remove this limitation
-		}
 
 		// Step 1. Extract the underlying JSON column from MVIndex Info.
 		mvIndex := ds.possibleAccessPaths[idx].Index
@@ -635,6 +631,20 @@ func (ds *DataSource) generateIndexMergeJSONMVIndexPath(normalPathCnt int, filte
 			}
 			indexMergePath := ds.buildIndexMergeOrPath(filters, partialPaths, filterIdx)
 			indexMergePath.IndexMergeIsIntersection = indexMergeIsIntersection
+
+			// Step 2.4. Update the estimated rows.
+			// TODO: use a naive estimation strategy here now for simplicity, make it more accurate.
+			minEstRows, maxEstRows := math.MaxFloat64, -1.0
+			for _, p := range indexMergePath.PartialIndexPaths {
+				minEstRows = math.Min(minEstRows, p.CountAfterAccess)
+				maxEstRows = math.Max(maxEstRows, p.CountAfterAccess)
+			}
+			if indexMergePath.IndexMergeIsIntersection {
+				indexMergePath.CountAfterAccess = minEstRows
+			} else {
+				indexMergePath.CountAfterAccess = maxEstRows
+			}
+
 			mvIndexPaths = append(mvIndexPaths, indexMergePath)
 		}
 	}

planner/core/indexmerge_path_test.go

@@ -51,3 +51,30 @@ index j1((cast(j1 as signed array))))`)
 		result.Check(testkit.Rows(output[i].Plan...))
 	}
 }
+
+func TestMVIndexSelection(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec(`create table t(a int, j json,
+index i_int((cast(j->'$.int' as signed array))))`)
+
+	var input []string
+	var output []struct {
+		SQL  string
+		Plan []string
+	}
+	planSuiteData := core.GetIndexMergeSuiteData()
+	planSuiteData.LoadTestCases(t, &input, &output)
+
+	for i, query := range input {
+		testdata.OnRecord(func() {
+			output[i].SQL = query
+		})
+		result := tk.MustQuery("explain format = 'brief' " + query)
+		testdata.OnRecord(func() {
+			output[i].Plan = testdata.ConvertRowsToStrings(result.Rows())
+		})
+		result.Check(testkit.Rows(output[i].Plan...))
+	}
+}

planner/core/testdata/index_merge_suite_in.json

@@ -21,6 +21,20 @@
       "select /*+ use_index_merge(t, j0_0) */ * from t where json_overlaps('1', (j0->'$.path0')) and a<10"
     ]
   },
+  {
+    "name": "TestMVIndexSelection",
+    "cases": [
+      "select (j->'$.int') from t where (1 member of (j->'$.int'))",
+      "select * from t where (1 member of (j->'$.int'))",
+      "select * from t where (1 member of (j->'$.int')) and a<10",
+      "select (j->'$.int') from t where json_contains((j->'$.int'), '[1, 2, 3]')",
+      "select * from t where json_contains((j->'$.int'), '[1, 2, 3]')",
+      "select * from t where json_contains((j->'$.int'), '[1, 2, 3]') and a<10",
+      "select (j->'$.int') from t where json_overlaps((j->'$.int'), '[1, 2, 3]')",
+      "select * from t where json_overlaps((j->'$.int'), '[1, 2, 3]')",
+      "select * from t where json_overlaps((j->'$.int'), '[1, 2, 3]') and a<10"
+    ]
+  },
   {
     "name": "TestIndexMergePathGeneration",
     "cases": [