executor: handle missing timestamp value for load data

[imtbkcat]

What problem does this PR solve?

fix #10504
LOAD DATA has different behavior with MySQL when handling missing timestamp/datetime value.

For example:
If we create a table:

create table t_default(id int, t timestamp null);
load data local infile "~/1.csv" into table t_default;

// 1.csv
12

The result for MySQL and TiDB are same:

mysql> select * from t_default;
+------+------+
| id   | t    |
+------+------+
|   12 | NULL |
+------+------+
1 row in set (0.00 sec)

But if t is NOT NULL, things are different.

create table t_default(id int, t timestamp not null default current_timestamp);
load data local infile "~/1.csv" into table t_default;

TiDB:

mysql> select * from t_default;
+------+---------------------+
| id   | t                   |
+------+---------------------+
|   12 | 0000-00-00 00:00:00 |
+------+---------------------+
1 row in set (0.00 sec)

MySQL:

mysql> select * from test.t_default;
+------+---------------------+
| id   | t                   |
+------+---------------------+
|   12 | 2019-07-05 13:27:05 |
+------+---------------------+
1 row in set (0.00 sec)

What is changed and how it works?

Add check for missing timestamp columns when insert load data.
If these columns have NOT NULL flag, set them to CURRENT_TIMESTAMP.

Check List

Tests

• Unit test

Side effects

• Increased code complexity

Related changes

• Need to cherry-pick to the release branch

[codecov]

Codecov Report

Merging #11093 into master will decrease coverage by 0.1194%.
The diff coverage is 20%.

@@               Coverage Diff               @@
##             master    #11093        +/-   ##
===============================================
- Coverage   81.1334%   81.014%   -0.1195%     
===============================================
  Files           419       419                
  Lines         90801     89324      -1477     
===============================================
- Hits          73670     72365      -1305     
+ Misses        11877     11720       -157     
+ Partials       5254      5239        -15

[codecov]

Codecov Report

Merging #11093 into master will increase coverage by 0.0314%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##             master    #11093        +/-   ##
===============================================
+ Coverage   81.2235%   81.255%   +0.0314%     
===============================================
  Files           423       423                
  Lines         90230     90056       -174     
===============================================
- Hits          73288     73175       -113     
+ Misses        11634     11579        -55     
+ Partials       5308      5302         -6

[crazycs520]

Could you add unit test?

[imtbkcat]

@crazycs520 test case will be added right now.

[imtbkcat]

/run-all-tests

[jackysp]

It is better to use IsTypeTime.

[imtbkcat]

PTAL @crazycs520

[jackysp]

LGTM

[jackysp]

PTAL @crazycs520

[imtbkcat]

/run-all-tests

[lysu]

LGTM