plan: always clone Expression when set it to plan.

executor/join_test.go

@@ -254,6 +254,15 @@ func (s *testSuite) TestJoin(c *C) {
 	result = tk.MustQuery("select /*+ TIDB_HJ(s, r) */ * from t as s join t as r on s.a = r.a limit 1;")
 	result.Check(testkit.Rows("1 1"))
 	plan.JoinConcurrency = savedConcurrency
+
+	tk.MustExec("drop table if exists user, aa, bb")
+	tk.MustExec("create table aa(id int)")
+	tk.MustExec("insert into aa values(1)")
+	tk.MustExec("create table bb(id int)")
+	tk.MustExec("insert into bb values(1)")
+	tk.MustExec("create table user(id int, name varchar(20))")
+	tk.MustExec("insert into user values(1, 'a'), (2, 'b')")
+	tk.MustQuery("select user.id,user.name from user left join aa on aa.id = user.id left join bb on aa.id = bb.id where bb.id < 10;").Check(testkit.Rows("1 a"))
 }
 
 func (s *testSuite) TestJoinCast(c *C) {

plan/predicate_push_down.go

@@ -133,8 +133,14 @@ func (p *LogicalJoin) PredicatePushDown(predicates []expression.Expression) (ret
 	case InnerJoin:
 		p.LeftConditions = nil
 		p.RightConditions = nil
-		p.EqualConditions = equalCond
-		p.OtherConditions = otherCond
+		p.EqualConditions = make([]*expression.ScalarFunction, 0, len(equalCond))
+		for _, cond := range equalCond {
+			p.EqualConditions = append(p.EqualConditions, cond.Clone().(*expression.ScalarFunction))
+		}
+		p.OtherConditions = make([]expression.Expression, 0, len(otherCond))
+		for _, cond := range otherCond {
+			p.OtherConditions = append(p.OtherConditions, cond.Clone())
+		}
 		leftCond = leftPushCond
 		rightCond = rightPushCond
 	}