broken merge join generated when TIDB_SMJ hint is specified

[eurekaka]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

mysql> select /*+ TIDB_SMJ(t1, t2) */ * from t t1 join t t2;
ERROR 1105 (HY000): Invalid arguments: Empty arguments detected.

mysql> explain select /*+ TIDB_SMJ(t1, t2) */ * from t t1 join t t2;
+-----------------------+-------+------+-------------------------------------------------------------+
| id                    | count | task | operator info                                               |
+-----------------------+-------+------+-------------------------------------------------------------+
| MergeJoin_6           | 4.00  | root | inner join                                                  |
| ├─TableReader_8       | 2.00  | root | data:TableScan_7                                            |
| │ └─TableScan_7       | 2.00  | cop  | table:t1, range:[-inf,+inf], keep order:false, stats:pseudo |
| └─TableReader_10      | 2.00  | root | data:TableScan_9                                            |
|   └─TableScan_9       | 2.00  | cop  | table:t2, range:[-inf,+inf], keep order:false, stats:pseudo |
+-----------------------+-------+------+-------------------------------------------------------------+
5 rows in set (0.00 sec)

2. What did you expect to see?

We should not generate merge join for this query, because it has no column equal condition.

3. What did you see instead?

Merge join is generated, but it cannot be executed.

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

[root@bogon ~/go/src/github.com/pingcap/tidb]$ ./bin/tidb-server -V
Release Version: v2.1.0-rc.3-426-g8468e7e
Git Commit Hash: 8468e7ec515bac8bda78e9ee2dcfe887d6446a42
Git Branch: master
UTC Build Time: 2019-01-10 11:27:29
GoVersion: go version go1.11.2 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false