stats: resolve the constant selectivity when handling DNF exprs (ping…

…cap#31242)

close pingcap#31096

planner/core/integration_test.go

@@ -5195,3 +5195,41 @@ func (s *testIntegrationSuite) TestIssue20510(c *C) {
 		"4 2 <nil> <nil>",
 	))
 }
+
+// TestDNFCondSelectivityWithConst test selectivity calculation with DNF conditions with one is const.
+// Close https://github.com/pingcap/tidb/issues/31096
+func (s *testIntegrationSuite) TestDNFCondSelectivityWithConst(c *C) {
+	testKit := testkit.NewTestKit(c, s.store)
+	testKit.MustExec("use test")
+	testKit.MustExec("drop table if exists t1")
+	testKit.MustExec("create table t1(a int, b int, c int);")
+	testKit.MustExec("insert into t1 value(10,10,10)")
+	for i := 0; i < 7; i++ {
+		testKit.MustExec("insert into t1 select * from t1")
+	}
+	testKit.MustExec("insert into t1 value(1,1,1)")
+	testKit.MustExec("analyze table t1")
+
+	testKit.MustQuery("explain select * from t1 where a=1 or b=1;").Check(testkit.Rows("TableReader_7 1.99 root  data:Selection_6]\n" +
+		"[└─Selection_6 1.99 cop[tikv]  or(eq(test.t1.a, 1), eq(test.t1.b, 1))]\n" +
+		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
+	testKit.MustQuery("explain select * from t1 where 0=1 or a=1 or b=1;").Check(testkit.Rows("TableReader_7 1.99 root  data:Selection_6]\n" +
+		"[└─Selection_6 1.99 cop[tikv]  or(0, or(eq(test.t1.a, 1), eq(test.t1.b, 1)))]\n" +
+		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
+	testKit.MustQuery("explain select * from t1 where null or a=1 or b=1;").Check(testkit.Rows("TableReader_7 1.99 root  data:Selection_6]\n" +
+		"[└─Selection_6 1.99 cop[tikv]  or(0, or(eq(test.t1.a, 1), eq(test.t1.b, 1)))]\n" +
+		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
+	testKit.MustQuery("explain select * from t1 where a=1 or false or b=1;").Check(testkit.Rows("TableReader_7 1.99 root  data:Selection_6]\n" +
+		"[└─Selection_6 1.99 cop[tikv]  or(eq(test.t1.a, 1), or(0, eq(test.t1.b, 1)))]\n" +
+		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
+	testKit.MustQuery("explain select * from t1 where a=1 or b=1 or \"false\";").Check(testkit.Rows("TableReader_7 1.99 root  data:Selection_6]\n" +
+		"[└─Selection_6 1.99 cop[tikv]  or(eq(test.t1.a, 1), or(eq(test.t1.b, 1), 0))]\n" +
+		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
+	testKit.MustQuery("explain select * from t1 where 1=1 or a=1 or b=1;").Check(testkit.Rows("TableReader_7 129.00 root  data:Selection_6]\n" +
+		"[└─Selection_6 129.00 cop[tikv]  or(1, or(eq(test.t1.a, 1), eq(test.t1.b, 1)))]\n" +
+		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
+	testKit.MustQuery("explain select * from t1 where a=1 or b=1 or 1=1;").Check(testkit.Rows("TableReader_7 129.00 root  data:Selection_6]\n" +
+		"[└─Selection_6 129.00 cop[tikv]  or(eq(test.t1.a, 1), or(eq(test.t1.b, 1), 1))]\n" +
+		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
+	testKit.MustExec("drop table if exists t1")
+}

planner/core/testdata/integration_suite_out.json

@@ -355,8 +355,8 @@
       {
         "SQL": "explain format = 'brief' select /*+ USE_INDEX_MERGE(t, a, b, c) */ * from t where 1 or t.a = 1 or t.b = 2",
         "Plan": [
-          "TableReader 8000.40 root  data:Selection",
-          "└─Selection 8000.40 cop[tikv]  or(1, or(eq(test.t.a, 1), eq(test.t.b, 2)))",
+          "TableReader 10000.00 root  data:Selection",
+          "└─Selection 10000.00 cop[tikv]  or(1, or(eq(test.t.a, 1), eq(test.t.b, 2)))",
           "  └─TableFullScan 10000.00 cop[tikv] table:t keep order:false, stats:pseudo"
         ]
       }

statistics/selectivity.go

@@ -354,6 +354,24 @@ func (coll *HistColl) Selectivity(ctx sessionctx.Context, exprs []expression.Exp
 				if ok {
 					continue
 				}
+				// where {"0" / 0 / "false" / false / null} or A or B ... the '0' constant item should be ignored.
+				if c, ok := cond.(*expression.Constant); ok {
+					if !expression.MaybeOverOptimized4PlanCache(ctx, []expression.Expression{cond}) {
+						if c.Value.IsNull() {
+							// constant is null
+							continue
+						}
+						if isTrue, err := c.Value.ToBool(sc); err == nil {
+							if isTrue == 0 {
+								// constant == 0
+								continue
+							}
+							// constant == 1
+							selectivity = 1.0
+							break
+						}
+					}
+				}
 
 				var cnfItems []expression.Expression
 				if scalar, ok := cond.(*expression.ScalarFunction); ok && scalar.FuncName.L == ast.LogicAnd {
@@ -365,7 +383,7 @@ func (coll *HistColl) Selectivity(ctx sessionctx.Context, exprs []expression.Exp
 				curSelectivity, _, err := coll.Selectivity(ctx, cnfItems, nil)
 				if err != nil {
 					logutil.BgLogger().Debug("something wrong happened, use the default selectivity", zap.Error(err))
-					selectivity = selectionFactor
+					curSelectivity = selectionFactor
 				}
 
 				selectivity = selectivity + curSelectivity - selectivity*curSelectivity