planner: avoid using index_merge when there are multiple table filters

planner/core/integration_test.go

@@ -1429,13 +1429,10 @@ func (s *testIntegrationSerialSuite) TestIndexMerge(c *C) {
 	tk.MustQuery("show warnings").Check(testkit.Rows())
 
 	tk.MustQuery("desc select /*+ use_index_merge(t) */ * from t where (a=1 and length(b)=1) or (b=1 and length(a)=1)").Check(testkit.Rows(
-		"Projection_4 1.60 root  test.t.a, test.t.b",
-		"└─IndexMerge_9 1.60 root  ",
-		"  ├─IndexRangeScan_5(Build) 1.00 cop[tikv] table:t, index:a(a) range:[1,1], keep order:false, stats:pseudo",
-		"  ├─IndexRangeScan_6(Build) 1.00 cop[tikv] table:t, index:b(b) range:[1,1], keep order:false, stats:pseudo",
-		"  └─Selection_8(Probe) 1.60 cop[tikv]  eq(length(cast(test.t.a)), 1), eq(length(cast(test.t.b)), 1)",
-		"    └─TableRowIDScan_7 2.00 cop[tikv] table:t keep order:false, stats:pseudo"))
-	tk.MustQuery("show warnings").Check(testkit.Rows())
+		"TableReader_7 1.60 root  data:Selection_6",
+		"└─Selection_6 1.60 cop[tikv]  or(and(eq(test.t.a, 1), eq(length(cast(test.t.b)), 1)), and(eq(test.t.b, 1), eq(length(cast(test.t.a)), 1)))",
+		"  └─TableFullScan_5 10000.00 cop[tikv] table:t keep order:false, stats:pseudo"))
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 IndexMerge is inapplicable or disabled"))
 }
 
 func (s *testIntegrationSerialSuite) TestIssue16407(c *C) {
@@ -2358,3 +2355,40 @@ func (s *testIntegrationSuite) TestIssue22040(c *C) {
 		c.Assert(errors.Cause(err), FitsTypeOf, expression.ErrOperandColumns)
 	}
 }
+
+func (s *testIntegrationSuite) TestIssue22105(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec(`CREATE TABLE t1 (
+  key1 int(11) NOT NULL,
+  key2 int(11) NOT NULL,
+  key3 int(11) NOT NULL,
+  key4 int(11) NOT NULL,
+  key5 int(11) DEFAULT NULL,
+  key6 int(11) DEFAULT NULL,
+  key7 int(11) NOT NULL,
+  key8 int(11) NOT NULL,
+  KEY i1 (key1),
+  KEY i2 (key2),
+  KEY i3 (key3),
+  KEY i4 (key4),
+  KEY i5 (key5),
+  KEY i6 (key6)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin`)
+
+	var input []string
+	var output []struct {
+		SQL  string
+		Plan []string
+	}
+	s.testData.GetTestCases(c, &input, &output)
+	for i, tt := range input {
+		s.testData.OnRecord(func() {
+			output[i].SQL = tt
+			output[i].Plan = s.testData.ConvertRowsToStrings(tk.MustQuery(tt).Rows())
+		})
+		tk.MustQuery(tt).Check(testkit.Rows(output[i].Plan...))
+	}
+}

planner/core/stats.go

@@ -426,6 +426,9 @@ func (ds *DataSource) generateIndexMergeOrPaths() {
 		}
 		if len(partialPaths) > 1 {
 			possiblePath := ds.buildIndexMergeOrPath(partialPaths, i)
+			if possiblePath == nil {
+				return
+			}
 
 			accessConds := make([]expression.Expression, 0, len(partialPaths))
 			for _, p := range partialPaths {
@@ -554,8 +557,15 @@ func (ds *DataSource) buildIndexMergeOrPath(partialPaths []*util.AccessPath, cur
 	indexMergePath := &util.AccessPath{PartialIndexPaths: partialPaths}
 	indexMergePath.TableFilters = append(indexMergePath.TableFilters, ds.pushedDownConds[:current]...)
 	indexMergePath.TableFilters = append(indexMergePath.TableFilters, ds.pushedDownConds[current+1:]...)
+	tableFilterCnt := 0
 	for _, path := range partialPaths {
+		// IndexMerge should not be used when the SQL is like 'select x from t WHERE (key1=1 AND key2=2) OR (key1=4 AND key3=6);'.
+		// Check issue https://github.com/pingcap/tidb/issues/22105 for details.
 		if len(path.TableFilters) > 0 {
+			tableFilterCnt++
+			if tableFilterCnt > 1 {
+				return nil
+			}
 			indexMergePath.TableFilters = append(indexMergePath.TableFilters, path.TableFilters...)
 		}
 	}

planner/core/testdata/integration_suite_in.json

@@ -242,5 +242,11 @@
       "explain select * from t2 where a >= 2.5 and a <= 2.5 order by b limit 2",
       "explain select * from t3 where a >= 'a' and a <= 'a' and b = 'b' and c > 'c'"
     ]
+  },
+  {
+    "name": "TestIssue22105",
+    "cases": [
+      "explain SELECT /*+ use_index_merge(t1)*/ COUNT(*) FROM t1 WHERE (key4=42 AND key6 IS NOT NULL) OR (key1=4 AND key3=6)"
+    ]
   }
 ]

planner/core/testdata/integration_suite_out.json

@@ -1348,5 +1348,20 @@
         ]
       }
     ]
+  },
+  {
+    "Name": "TestIssue22105",
+    "Cases": [
+      {
+        "SQL": "explain SELECT /*+ use_index_merge(t1)*/ COUNT(*) FROM t1 WHERE (key4=42 AND key6 IS NOT NULL) OR (key1=4 AND key3=6)",
+        "Plan": [
+          "StreamAgg_20 1.00 root  funcs:count(Column#12)->Column#10",
+          "└─TableReader_21 1.00 root  data:StreamAgg_9",
+          "  └─StreamAgg_9 1.00 cop[tikv]  funcs:count(1)->Column#12",
+          "    └─Selection_19 10.00 cop[tikv]  or(and(eq(test.t1.key4, 42), not(isnull(test.t1.key6))), and(eq(test.t1.key1, 4), eq(test.t1.key3, 6)))",
+          "      └─TableFullScan_18 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"
+        ]
+      }
+    ]
   }
 ]