types,expression: Fix parse time from string

[spongedu]

What problem does this PR solve?

What is changed and how it works?

Currently TiDB fail to deal with some cases when parse string to datetime, This pr fixes these cases. For example, in MySQL:

mysql> select cast("1701020301" as datetime);
+--------------------------------+
| cast("1701020301" as datetime) |
+--------------------------------+
| 2017-01-02 03:01:00            |
+--------------------------------+
1 row in set (0.00 sec)

mysql> select cast("170102034" as datetime);
+-------------------------------+
| cast("170102034" as datetime) |
+-------------------------------+
| 2017-01-02 03:04:00           |
+-------------------------------+
1 row in set (0.00 sec)

While in TiDB:

tidb> select cast("1701020301." as datetime);
ERROR 1105 (HY000): invalid time format
tidb> select cast("1701020301" as datetime);
ERROR 1105 (HY000): invalid time format
tidb> select cast("170102034" as datetime);
ERROR 1105 (HY000): invalid time format

Check List

Tests

• Unit test
• Integration test

[eurekaka]

should we raise warning as MySQL does for the case below?

mysql> select cast("170102037.1122" as datetime);
+------------------------------------+
| cast("170102037.1122" as datetime) |
+------------------------------------+
| 2017-01-02 03:07:11                |
+------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+------------------------------------------------------+
| Level   | Code | Message                                              |
+---------+------+------------------------------------------------------+
| Warning | 1292 | Truncated incorrect datetime value: '170102037.1122' |
+---------+------+------------------------------------------------------+
1 row in set (0.00 sec)

[spongedu]

Yes, indeed. I'll fix here

[zz-jason]

@spongedu We use go 1.11 now, maybe you can update go to make fmt happy.

[spongedu]

@zz-jason ok

[spongedu]

@zz-jason done here. PTAL

[eurekaka]

/run-all-tests

[eurekaka]

LGTM

[zz-jason]

LGTM