please support savepoint

[aesirteam]

Please answer these questions before submitting your issue. Thanks!

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

START TRANSACTION;
SELECT 1 FROM dual;
SAVEPOINT save1;
SELECT 1 FROM dual;
ROLLBACK TO SAVEPOINT save1;
COMMIT;

2. What did you expect to see?

All statements succeed.

3. What did you see instead?

mysql> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT 1 FROM dual;
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

mysql> SAVEPOINT save1;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your TiDB version for the right syntax to use line 1 column 9 near "SAVEPOINT save1" 
mysql> SELECT 1 FROM dual;
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

mysql> ROLLBACK TO SAVEPOINT save1;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your TiDB version for the right syntax to use line 1 column 11 near "TO SAVEPOINT save1" 
mysql> COMMIT;
Query OK, 0 rows affected (0.00 sec)

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   Release Version: v2.1.0-alpha-48-ge2c8c4e
   Git Commit Hash: e2c8c4e
   Git Branch: master
   UTC Build Time: 2018-06-13 12:05:19
   GoVersion: go version go1.10.2 linux/amd64
   Race Enabled: false
   TiKV Min Version: 2.1.0-alpha.1-c4133d3ef0f099f8716a916c198390b26293ec00

[zimulala]

@aesirteam
We don't support savepoint, and it isn't on our roadmap now.

[breezewish]

Duplicate with #3663

[muyu66]

Why don't support? I think it's important to implement Sequelize's Callback transaction

[lysu]

@muyu66 yes, savepoint is a very useful feature, it's not on our short-term roadmap, but we maybe try to implement that in future, and welcome to contribute too~

[ihipop]

@lysu pingcap/docs#682 this pull just add the compatibility of savepoint,not the function implementation of savepoint,is it right?

[lysu]

@ihipop , yes , savepoint isn't supported until now..

[chris-ng-scmp]

Good to see if savepoint can be supported