planner: refine function accessPathsForConds to avoid wrong indexmerge plan (#16863)

planner/core/integration_test.go

@@ -905,3 +905,17 @@ func (s *testIntegrationSuite) TestIssue15858(c *C) {
 	tk.MustExec("create table t(a int primary key)")
 	tk.MustExec("select * from t t1, (select a from t order by a+1) t2 where t1.a = t2.a")
 }
+
+func (s *testIntegrationSerialSuite) TestIssue16837(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,b int,c int,d int,e int,unique key idx_ab(a,b),unique key(c),unique key(d))")
+	tk.MustQuery("explain select /*+ use_index_merge(t,c,idx_ab) */ * from t where a = 1 or (e = 1 and c = 1)").Check(testkit.Rows(
+		"TableReader_7 8000.00 root  data:Selection_6",
+		"└─Selection_6 8000.00 cop[tikv]  or(eq(test.t.a, 1), and(eq(test.t.e, 1), eq(test.t.c, 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"))
+	tk.MustExec("insert into t values (2, 1, 1, 1, 2)")
+	tk.MustQuery("select /*+ use_index_merge(t,c,idx_ab) */ * from t where a = 1 or (e = 1 and c = 1)").Check(testkit.Rows())
+}

planner/core/stats.go

@@ -378,6 +378,14 @@ 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.TableFilters) > 0 || len(path.AccessConds) == 0 {
+				// If AccessConds is empty or tableFilter is not empty, we ignore the access path.
+				// Now these conditions are too strict.
+				// For example, a sql `select * from t where a > 1 or (b < 2 and c > 3)` and table `t` with indexes
+				// on a and b separately. we can generate a `IndexMergePath` with table filter `a > 1 or (b < 2 and c > 3)`.
+				// TODO: solve the above case
+				continue
+			}
 			// If we have point or empty range, just remove other possible paths.
 			if noIntervalRanges || len(path.Ranges) == 0 {
 				if len(results) == 0 {
@@ -399,6 +407,14 @@ func (ds *DataSource) accessPathsForConds(conditions []expression.Expression, us
 				continue
 			}
 			noIntervalRanges := ds.deriveIndexPathStats(path, conditions, true)
+			if len(path.TableFilters) > 0 || len(path.AccessConds) == 0 {
+				// If AccessConds is empty or tableFilter is not empty, we ignore the access path.
+				// Now these conditions are too strict.
+				// For example, a sql `select * from t where a > 1 or (b < 2 and c > 3)` and table `t` with indexes
+				// on a and b separately. we can generate a `IndexMergePath` with table filter `a > 1 or (b < 2 and c > 3)`.
+				// TODO: solve the above case
+				continue
+			}
 			// If we have empty range, or point range on unique index, just remove other possible paths.
 			if (noIntervalRanges && path.Index.Unique) || len(path.Ranges) == 0 {
 				if len(results) == 0 {
@@ -410,14 +426,6 @@ func (ds *DataSource) accessPathsForConds(conditions []expression.Expression, us
 				break
 			}
 		}
-		// If AccessConds is empty or tableFilter is not empty, we ignore the access path.
-		// Now these conditions are too strict.
-		// For example, a sql `select * from t where a > 1 or (b < 2 and c > 3)` and table `t` with indexes
-		// on a and b separately. we can generate a `IndexMergePath` with table filter `a > 1 or (b < 2 and c > 3)`.
-		// TODO: solve the above case
-		if len(path.TableFilters) > 0 || len(path.AccessConds) == 0 {
-			continue
-		}
 		results = append(results, path)
 	}
 	return results