planner: add missing CanExprsPushDown checks when generating IndexMerge path for or (#41361)

planner/core/integration_test.go

@@ -6713,3 +6713,28 @@ func TestAutoIncrementCheckWithCheckConstraint(t *testing.T) {
 		KEY idx_autoinc_id (id)
 	)`)
 }
+
+// https://github.com/pingcap/tidb/issues/41273
+func TestIssue41273(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec(`CREATE TABLE t (
+    	a set('nwbk','r5','1ad3u','van','ir1z','y','9m','f1','z','e6yd','wfev') NOT NULL DEFAULT 'ir1z,f1,e6yd',
+    	b enum('soo2','4s4j','qi9om','8ue','i71o','qon','3','3feh','6o1i','5yebx','d') NOT NULL DEFAULT '8ue',
+    	c varchar(66) DEFAULT '13mdezixgcn',
+    	PRIMARY KEY (a,b) /*T![clustered_index] CLUSTERED */,
+    	UNIQUE KEY ib(b),
+    	KEY ia(a)
+    )ENGINE=InnoDB DEFAULT CHARSET=ascii COLLATE=ascii_bin;`)
+	tk.MustExec("INSERT INTO t VALUES('ir1z,f1,e6yd','i71o','13mdezixgcn'),('ir1z,f1,e6yd','d','13mdezixgcn'),('nwbk','8ue','13mdezixgcn');")
+	expectedRes := []string{"ir1z,f1,e6yd d 13mdezixgcn", "ir1z,f1,e6yd i71o 13mdezixgcn", "nwbk 8ue 13mdezixgcn"}
+	tk.MustQuery("select * from t where a between 'e6yd' and 'z' or b <> '8ue';").Sort().Check(testkit.Rows(expectedRes...))
+	tk.MustQuery("select /*+ use_index_merge(t) */ * from t where a between 'e6yd' and 'z' or b <> '8ue';").Sort().Check(testkit.Rows(expectedRes...))
+	// For now tidb doesn't support push set type to TiKV, and column a is a set type, so we shouldn't generate a IndexMerge path.
+	require.False(t,
+		tk.HasPlan("select /*+ use_index_merge(t) */ * from t where a between 'e6yd' and 'z' or b <> '8ue'",
+			"IndexMerge"),
+	)
+}

planner/core/stats.go

@@ -557,11 +557,28 @@ func (ds *DataSource) generateIndexMergeOrPaths(filters []expression.Expression)
 		if !ok || sf.FuncName.L != ast.LogicOr {
 			continue
 		}
+		// shouldKeepCurrentFilter means the partial paths can't cover the current filter completely, so we must add
+		// the current filter into a Selection after partial paths.
+		shouldKeepCurrentFilter := false
 		var partialPaths = make([]*util.AccessPath, 0, usedIndexCount)
 		dnfItems := expression.FlattenDNFConditions(sf)
 		for _, item := range dnfItems {
 			cnfItems := expression.SplitCNFItems(item)
-			itemPaths := ds.accessPathsForConds(cnfItems, usedIndexCount)
+
+			pushedDownCNFItems := make([]expression.Expression, 0, len(cnfItems))
+			for _, cnfItem := range cnfItems {
+				if expression.CanExprsPushDown(ds.ctx.GetSessionVars().StmtCtx,
+					[]expression.Expression{cnfItem},
+					ds.ctx.GetClient(),
+					kv.TiKV,
+				) {
+					pushedDownCNFItems = append(pushedDownCNFItems, cnfItem)
+				} else {
+					shouldKeepCurrentFilter = true
+				}
+			}
+
+			itemPaths := ds.accessPathsForConds(pushedDownCNFItems, usedIndexCount)
 			if len(itemPaths) == 0 {
 				partialPaths = nil
 				break
@@ -588,7 +605,7 @@ func (ds *DataSource) generateIndexMergeOrPaths(filters []expression.Expression)
 			continue
 		}
 		if len(partialPaths) > 1 {
-			possiblePath := ds.buildIndexMergeOrPath(filters, partialPaths, i)
+			possiblePath := ds.buildIndexMergeOrPath(filters, partialPaths, i, shouldKeepCurrentFilter)
 			if possiblePath == nil {
 				return nil
 			}
@@ -726,28 +743,32 @@ func (ds *DataSource) buildIndexMergePartialPath(indexAccessPaths []*util.Access
 }
 
 // buildIndexMergeOrPath generates one possible IndexMergePath.
-func (ds *DataSource) buildIndexMergeOrPath(filters []expression.Expression, partialPaths []*util.AccessPath, current int) *util.AccessPath {
+func (ds *DataSource) buildIndexMergeOrPath(
+	filters []expression.Expression,
+	partialPaths []*util.AccessPath,
+	current int,
+	shouldKeepCurrentFilter bool,
+) *util.AccessPath {
 	indexMergePath := &util.AccessPath{PartialIndexPaths: partialPaths}
 	indexMergePath.TableFilters = append(indexMergePath.TableFilters, filters[:current]...)
 	indexMergePath.TableFilters = append(indexMergePath.TableFilters, filters[current+1:]...)
-	var addCurrentFilter bool
 	for _, path := range partialPaths {
 		// If any partial path contains table filters, we need to keep the whole DNF filter in the Selection.
 		if len(path.TableFilters) > 0 {
-			addCurrentFilter = true
+			shouldKeepCurrentFilter = true
 		}
 		// If any partial path's index filter cannot be pushed to TiKV, we should keep the whole DNF filter.
 		if len(path.IndexFilters) != 0 && !expression.CanExprsPushDown(ds.ctx.GetSessionVars().StmtCtx, path.IndexFilters, ds.ctx.GetClient(), kv.TiKV) {
-			addCurrentFilter = true
+			shouldKeepCurrentFilter = true
 			// Clear IndexFilter, the whole filter will be put in indexMergePath.TableFilters.
 			path.IndexFilters = nil
 		}
 		if len(path.TableFilters) != 0 && !expression.CanExprsPushDown(ds.ctx.GetSessionVars().StmtCtx, path.TableFilters, ds.ctx.GetClient(), kv.TiKV) {
-			addCurrentFilter = true
+			shouldKeepCurrentFilter = true
 			path.TableFilters = nil
 		}
 	}
-	if addCurrentFilter {
+	if shouldKeepCurrentFilter {
 		indexMergePath.TableFilters = append(indexMergePath.TableFilters, filters[current])
 	}
 	return indexMergePath