explicit_defaults_for_timestamp參數

Introduced	5.6.6
Deprecated	5.6.6
Command-Line Format	--explicit_defaults_for_timestamp=#
System Variable	Name	explicit_defaults_for_timestamp
	Variable Scope	Global, Session
	Dynamic Variable	No
Permitted Values	Type	boolean
	Default	FALSE

 在mysql中：
- timestamp列如果沒有顯式定義為null，默認會被設置為not null屬性。(其它的數據類型如果沒有顯式定義為not null，默認是可以為null的)。設置timestamp的列值為null，會自動存儲為當前timestamp
- 表中的第一個timestamp列，如果沒有定義為null、定義default值或者on update，會自動分配default current_timestamp和on update current_timestamp屬性
- 表中第一個timestamp列之后的所有timestamp列，如果沒有被定義為null、定義default值，會自動被指定默認值'0000-00-00 00:00:00'。在插入時，如果沒有指定這些列的值，會自動指定為'0000-00-00 00:00:00'，且不會產生警告

mysql> create table timestamp_eg(
    ->     id int not null auto_increment,
    ->     time1 timestamp,
    ->     time2 timestamp,
    ->     time3 timestamp NOT NULL DEFAULT '2010-01-01 00:00:00',
    ->     time4 timestamp,
    ->     primary key(id));
Query OK, 0 rows affected (0.01 sec)

mysql> insert into timestamp_eg(id) values(1);
Query OK, 1 row affected (0.00 sec)

mysql> select * from timestamp_eg;
+----+---------------------+---------------------+---------------------+---------------------+
| id | time1               | time2               | time3               | time4               |
+----+---------------------+---------------------+---------------------+---------------------+
|  1 | 2015-12-16 09:23:33 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 |
+----+---------------------+---------------------+---------------------+---------------------+
1 row in set (0.01 sec)

mysql> update timestamp_eg set id=2 where id=1;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from timestamp_eg;
+----+---------------------+---------------------+---------------------+---------------------+
| id | time1               | time2               | time3               | time4               |
+----+---------------------+---------------------+---------------------+---------------------+
|  2 | 2015-12-16 09:25:01 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 |
+----+---------------------+---------------------+---------------------+---------------------+
1 row in set (0.00 sec)

mysql> insert into timestamp_eg(id,time4) values(3,'2011-01-01 00:00:00');
Query OK, 1 row affected (0.00 sec)

mysql> select * from timestamp_eg;
+----+---------------------+---------------------+---------------------+---------------------+
| id | time1               | time2               | time3               | time4               |
+----+---------------------+---------------------+---------------------+---------------------+
|  2 | 2015-12-16 09:25:01 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 |
|  3 | 2015-12-16 09:28:04 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 2011-01-01 00:00:00 |
+----+---------------------+---------------------+---------------------+---------------------+
2 rows in set (0.00 sec)

mysql> update timestamp_eg set id=4 where id=3;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from timestamp_eg;
+----+---------------------+---------------------+---------------------+---------------------+
| id | time1               | time2               | time3               | time4               |
+----+---------------------+---------------------+---------------------+---------------------+
|  2 | 2015-12-16 09:25:01 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 |
|  4 | 2015-12-16 09:28:24 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 2011-01-01 00:00:00 |
+----+---------------------+---------------------+---------------------+---------------------+
2 rows in set (0.00 sec)

mysql> 

 

從MySQL5.6.6這種默認設置的方法被廢棄了。在MySQL啟動時會出現以下警告：

[Warning] TIMESTAMP with implicit DEFAULT value is deprecated.
Please use --explicit_defaults_for_timestamp server option (see
documentation for more details).

要想取消該警告，在啟動mysql時，my.cnf中加入

[mysqld]
explicit_defaults_for_timestamp=true

 

修改該參數后，timestamp類型的列的處理方式也會發生變化：

- timestamp列如果沒有顯式定義為not null，則支持null屬性。設置timestamp的列值為null，就不會被設置為current timestamp
- 不會自動分配default current_timestamp和on update current_timestamp屬性，這些屬性必須顯式指定
- 聲明為not null且沒有顯式指定默認值是沒有默認值的。表中插入列，又沒有給timestamp列賦值時，如果是嚴格sql模式，會拋出一個錯誤；如果嚴格sql模式沒有啟用，該列會賦值為’0000-00-00 00:00:00′，同時出現一個警告。（這和mysql處理其它時間類型數據一樣，如datetime）

mysql> create table timestamp_02(
    -> id int not null auto_increment,
    -> time1 timestamp not null,
    -> primary key(id)
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql> insert into timestamp_02(id) values(1);
ERROR 1364 (HY000): Field 'time1' doesn't have a default value
mysql>