expression: Fix some datetime related cases that is inconsistent with MySQL

[spongedu]

What problem does this PR solve?

This pr fixes some datetime related cases in TiDB that is inconsistent with MySQL.

1. Currently in TiDB, sql mode NO_ZERO_DATE is not taken into consideration in some builtin-time functions(month, dayofmonth, year, monthname). In MySQL, if NO_ZERO_DATE is not set, no error or warning should happen on zero datetime such as 0000-00-00 00:00:00.
   For example, in MySQL:

mysql> drop table t;
Query OK, 0 rows affected (0.03 sec)

mysql> create table t ( a bigint);                                                                                                                                                                          Query OK, 0 rows affected (0.04 sec)

mysql> select @@sql_mode;
+--------------------------------------------+
| @@sql_mode                                 |
+--------------------------------------------+
| STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION |
+--------------------------------------------+
1 row in set (0.00 sec)

mysql> insert into t select month("0000-00-00 00:00:00");
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> set sql_mode="NO_ZERO_DATE";                                                                                                                                                                         Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t select month("0000-00-00 00:00:00");
Query OK, 1 row affected, 1 warning (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 1

mysql> show warnings;
+---------+------+-------------------------------------------------+
| Level   | Code | Message                                         |
+---------+------+-------------------------------------------------+
| Warning | 1292 | Incorrect datetime value: '0000-00-00 00:00:00' |
+---------+------+-------------------------------------------------+
1 row in set (0.00 sec)

mysql> set sql_mode="NO_ZERO_DATE,STRICT_TRANS_TABLES";                                                                                                                                                     Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t select month("0000-00-00 00:00:00");                                                                                                                                                   ERROR 1292 (22007): Incorrect datetime value: '0000-00-00 00:00:00'

While in TiDB:

tidb> select @@sql_mode;
+--------------------------------------------+
| @@sql_mode                                 |
+--------------------------------------------+
| STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION |
+--------------------------------------------+
1 row in set (0.00 sec)

tidb> create table t ( a bigint);
Query OK, 0 rows affected (0.01 sec)

tidb> insert into t select month("0000-00-00 00:00:00");
ERROR 1292 (22007): Incorrect datetime value: '0000-00-00 00:00:00.000000'
tidb> set sql_mode="NO_ZERO_DATE";
Query OK, 0 rows affected (0.00 sec)

tidb> insert into t select month("0000-00-00 00:00:00");
Query OK, 1 row affected, 1 warning (0.00 sec)

tidb> show warnings;
+---------+------+--------------------------------------------------------+
| Level   | Code | Message                                                |
+---------+------+--------------------------------------------------------+
| Warning | 1292 | Incorrect datetime value: '0000-00-00 00:00:00.000000' |
+---------+------+--------------------------------------------------------+
1 row in set (0.00 sec)

tidb> set sql_mode="NO_ZERO_DATE,STRICT_TRANS_TABLES";
Query OK, 0 rows affected (0.00 sec)

tidb> insert into t select month("0000-00-00 00:00:00");
ERROR 1292 (22007): Incorrect datetime value: '0000-00-00 00:00:00.000000'

2. Currently in TiDB, float values are not correctly cast into datetime.
   For example, in MySQL:

mysql> select cast(20170118.999 as datetime);
+--------------------------------+
| cast(20170118.999 as datetime) |
+--------------------------------+
| 2017-01-18 00:00:00            |
+--------------------------------+
1 row in set (0.00 sec)

While in TiDB:

tidb> select cast(20170118.999 as datetime);
ERROR 1292 (22007): invalid time format: '99'

What is changed and how it works?

Changed the way some builtin_time functions deal with ZERO datetime

Check List

Tests

Unit tests && integration tests

[eurekaka]

LGTM

[eurekaka]

Any reason for removing the Trace?

[spongedu]

@eurekaka nope. This should be change by mistake. I'll fix here.

[zz-jason]

/run-all-tests

[zz-jason]

LGTM