run executor/join_test.go failed

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Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

In #11262, the unit test failed.

2. What did you expect to see?

no tests fail.

3. What did you see instead?

[2019-07-16T07:08:41.157Z] FAIL: join_test.go:511: testSuite2.TestSubquery
[2019-07-16T07:08:41.157Z] 
[2019-07-16T07:08:41.157Z] join_test.go:573:
[2019-07-16T07:08:41.157Z]     result.Check(testkit.Rows("1 2"))
[2019-07-16T07:08:41.157Z] /home/jenkins/workspace/tidb_ghpr_check_2/go/src/github.com/pingcap/tidb/util/testkit/testkit.go:61:
[2019-07-16T07:08:41.157Z]     res.c.Assert(resBuff.String(), check.Equals, needBuff.String(), res.comment)
[2019-07-16T07:08:41.157Z] ... obtained string = ""
[2019-07-16T07:08:41.157Z] ... expected string = "[1 2]\n"
[2019-07-16T07:08:41.157Z] ... sql:select * from a b where c = (select d from b a where a.c = 2 and b.c = 1), args:[]

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

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#19338 (comment)

[2020-08-24T11:13:21.026Z] FAIL: join_test.go:511: testSuite2.TestSubquery
[2020-08-24T11:13:21.026Z] 
[2020-08-24T11:13:21.026Z] join_test.go:643:
[2020-08-24T11:13:21.026Z]     result = tk.MustQuery("select (select id from s where s.id = t.id order by s.id) from t")
[2020-08-24T11:13:21.026Z] /home/jenkins/agent/workspace/tidb_ghpr_unit_test/go/src/github.com/pingcap/tidb/util/testkit/testkit.go:277:
[2020-08-24T11:13:21.026Z]     tk.c.Check(err, check.IsNil, comment)
[2020-08-24T11:13:21.026Z] ... value *errors.fundamental = subquery returns more than 1 row ("subquery returns more than 1 row")
[2020-08-24T11:13:21.026Z] ... sql:select (select id from s where s.id = t.id order by s.id) from t, args:[]
[2020-08-24T11:13:21.026Z] 
[2020-08-24T11:13:21.026Z] join_test.go:644:
[2020-08-24T11:13:21.026Z]     result.Check(testkit.Rows("2", "2"))
[2020-08-24T11:13:21.026Z] /home/jenkins/agent/workspace/tidb_ghpr_unit_test/go/src/github.com/pingcap/tidb/util/testkit/testkit.go:61:
[2020-08-24T11:13:21.026Z]     res.c.Assert(resBuff.String(), check.Equals, needBuff.String(), res.comment)
[2020-08-24T11:13:21.026Z] ... obtained string = ""
[2020-08-24T11:13:21.026Z] ... expected string = "" +
[2020-08-24T11:13:21.026Z] ...     "[2]\n" +
[2020-08-24T11:13:21.026Z] ...     "[2]\n"
[2020-08-24T11:13:21.026Z] ... sql:select (select id from s where s.id = t.id order by s.id) from t, args:[]