executor: do not build range for NullOuterVal in IndexLookUpJoin (pin…

…gcap#8505)

executor/index_lookup_join.go

@@ -472,7 +472,12 @@ func (iw *innerWorker) constructDatumLookupKey(task *lookUpJoinTask, rowIdx int)
 	dLookupKey := make([]types.Datum, 0, keyLen)
 	for i, keyCol := range iw.outerCtx.keyCols {
 		outerValue := outerRow.GetDatum(keyCol, iw.outerCtx.rowTypes[keyCol])
-
+		// Join-on-condition can be promised to be equal-condition in
+		// IndexNestedLoopJoin, thus the filter will always be false if
+		// outerValue is null, and we don't need to lookup it.
+		if outerValue.IsNull() {
+			return nil, nil
+		}
 		innerColType := iw.rowTypes[iw.keyCols[i]]
 		innerValue, err := outerValue.ConvertTo(sc, innerColType)
 		if err != nil {

executor/join_test.go

@@ -866,6 +866,23 @@ func (s *testSuite) TestIndexLookupJoin(c *C) {
 		`1 5 1 1`,
 		`1 6 1 2`,
 	))
+
+	tk.MustExec(`drop table if exists t1, t2, t3;`)
+	tk.MustExec("create table t1(a int primary key, b int)")
+	tk.MustExec("insert into t1 values(1, 0), (2, null)")
+	tk.MustExec("create table t2(a int primary key)")
+	tk.MustExec("insert into t2 values(0)")
+	tk.MustQuery("select /*+ TIDB_INLJ(t2)*/ * from t1 left join t2 on t1.b = t2.a;").Check(testkit.Rows(
+		`1 0 0`,
+		`2 <nil> <nil>`,
+	))
+
+	tk.MustExec("create table t3(a int, key(a))")
+	tk.MustExec("insert into t3 values(0)")
+	tk.MustQuery("select /*+ TIDB_INLJ(t3)*/ * from t1 left join t3 on t1.b = t3.a;").Check(testkit.Rows(
+		`1 0 0`,
+		`2 <nil> <nil>`,
+	))
 }
 
 func (s *testSuite) TestMergejoinOrder(c *C) {