MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp参数

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MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp参数

MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp参数:安装MySQL时，有warning: [root@localhost mysql]# scripts/mysql_install_db --user=mysql Installing MySQL system tables...2015-08-13 14:20:09 0 [Warning] TIMESTAMP with implicit DEFAU

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导读MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp参数:安装MySQL时，有warning: [root@localhost mysql]# scripts/mysql_install_db --user=mysql Installing MySQL system tables...2015-08-13 14:20:09 0 [Warning] TIMESTAMP with implicit DEFAU

安装MySQL时，有warning:

[root@localhost mysql]# scripts/mysql_install_db --user=mysql
Installing MySQL system tables...2015-08-13 14:20:09 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2015-08-13 14:20:09 0 [Note] ./bin/mysqld (mysqld 5.6.26) starting as process 1934 ...
2015-08-13 14:20:09 1934 [Note] InnoDB: Using mutexes to ref count buffer pool pages
2015-08-13 14:20:09 1934 [Note] InnoDB: The InnoDB memory heap is disabled
2015-08-13 14:20:09 1934 [Note] InnoDB: Mutexes and rw_locks use InnoDB's own implementation
2015-08-13 14:20:09 1934 [Note] InnoDB: Memory barrier is not used
2015-08-13 14:20:09 1934 [Note] InnoDB: Compressed tables use zlib 1.2.3
2015-08-13 14:20:09 1934 [Note] InnoDB: Using Linux native AIO
2015-08-13 14:20:09 1934 [Note] InnoDB: Not using CPU crc32 instructions
2015-08-13 14:20:09 1934 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2015-08-13 14:20:09 1934 [Note] InnoDB: Completed initialization of buffer pool
2015-08-13 14:20:10 1934 [Note] InnoDB: The first specified data file ./ibdata1 did not exist: a new database to be created!
2015-08-13 14:20:10 1934 [Note] InnoDB: Setting file ./ibdata1 size to 12 MB
2015-08-13 14:20:10 1934 [Note] InnoDB: Database physically writes the file full: wait...
2015-08-13 14:20:10 1934 [Note] InnoDB: Setting log file ./ib_logfile101 size to 48 MB
2015-08-13 14:20:11 1934 [Note] InnoDB: Setting log file ./ib_logfile1 size to 48 MB
2015-08-13 14:20:12 1934 [Note] InnoDB: Renaming log file ./ib_logfile101 to ./ib_logfile0
2015-08-13 14:20:12 1934 [Warning] InnoDB: New log files created, LSN=45781
2015-08-13 14:20:12 1934 [Note] InnoDB: Doublewrite buffer not found: creating new
2015-08-13 14:20:12 1934 [Note] InnoDB: Doublewrite buffer created
2015-08-13 14:20:12 1934 [Note] InnoDB: 128 rollback segment(s) are active.
2015-08-13 14:20:12 1934 [Warning] InnoDB: Creating foreign key constraint system tables.
2015-08-13 14:20:12 1934 [Note] InnoDB: Foreign key constraint system tables created
2015-08-13 14:20:12 1934 [Note] InnoDB: Creating tablespace and datafile system tables.
2015-08-13 14:20:12 1934 [Note] InnoDB: Tablespace and datafile system tables created.
2015-08-13 14:20:12 1934 [Note] InnoDB: Waiting for purge to start
2015-08-13 14:20:12 1934 [Note] InnoDB: 5.6.26 started; log sequence number 0
2015-08-13 14:20:14 1934 [Note] Binlog end
2015-08-13 14:20:14 1934 [Note] InnoDB: FTS optimize thread exiting.
2015-08-13 14:20:14 1934 [Note] InnoDB: Starting shutdown...
2015-08-13 14:20:16 1934 [Note] InnoDB: Shutdown completed; log sequence number 1625977

Filling help tables...2015-08-13 14:20:16 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. 
Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2015-08-13 14:20:16 0 [Note] ./bin/mysqld (mysqld 5.6.26) starting as process 1957 ...
2015-08-13 14:20:16 1957 [Note] InnoDB: Using mutexes to ref count buffer pool pages
2015-08-13 14:20:16 1957 [Note] InnoDB: The InnoDB memory heap is disabled
2015-08-13 14:20:16 1957 [Note] InnoDB: Mutexes and rw_locks use InnoDB's own implementation
2015-08-13 14:20:16 1957 [Note] InnoDB: Memory barrier is not used
2015-08-13 14:20:16 1957 [Note] InnoDB: Compressed tables use zlib 1.2.3
2015-08-13 14:20:16 1957 [Note] InnoDB: Using Linux native AIO
2015-08-13 14:20:16 1957 [Note] InnoDB: Not using CPU crc32 instructions
2015-08-13 14:20:16 1957 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2015-08-13 14:20:16 1957 [Note] InnoDB: Completed initialization of buffer pool
2015-08-13 14:20:16 1957 [Note] InnoDB: Highest supported file format is Barracuda.
2015-08-13 14:20:16 1957 [Note] InnoDB: 128 rollback segment(s) are active.
2015-08-13 14:20:16 1957 [Note] InnoDB: Waiting for purge to start
2015-08-13 14:20:16 1957 [Note] InnoDB: 5.6.26 started; log sequence number 1625977
2015-08-13 14:20:17 1957 [Note] Binlog end
2015-08-13 14:20:17 1957 [Note] InnoDB: FTS optimize thread exiting.
2015-08-13 14:20:17 1957 [Note] InnoDB: Starting shutdown...
2015-08-13 14:20:18 1957 [Note] InnoDB: Shutdown completed; log sequence number 1625987

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PLEASE REMEMBER TO SET A PASSWORD FOR THE MySQL root USER !
To do so, start the server, then issue the following commands:

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See the manual for more instructions.

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New default config file was created as ./my.cnf and
will be used by default by the server when you start it.
You may edit this file to change server settings

WARNING: Default config file /etc/my.cnf exists on the system
This file will be read by default by the MySQL server
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[root@localhost mysql]#

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

其原因是从 5.6开始，timestamp 的默认行为已经是 deprecated 了。

在MySQL 5.6.6之前，TIMESTAMP的默认行为：

TIMESTAMP列如果没有明确声明NULL属性，默认为NOT NULL。（而其他数据类型，如果没有显示声明为NOT NULL，则允许NULL值。）设置TIMESTAMP的列值为NULL，会自动存储为当前timestamp。

表中的第一个TIMESTAMP列，如果没有声明NULL属性、DEFAULT或者 ON UPDATE，会自动分配 DEFAULT CURRENT_TIMESTAMP和ON UPDATE CURRENT_TIMESTAMP 属性。

表中第二个TIMESTAMP列，如果没有声明为NULL或者DEFAULT子句，默认自动分配'0000-00-00 00:00:00′。插入行时没有指明改列的值，该列默认分配'0000-00-00 00:00:00′，且没有警告。
要关闭警告，需要加入下面的参数：

explicit_defaults_for_timestamp=true

重启MySQL后错误消失，这时TIMESTAMP的行为如下：

TIMESTAMP如果没有显示声明NOT NULL，是允许NULL值的，可以直接设置改列为NULL，而没有默认填充行为。
TIMESTAMP不会默认分配DEFAULT CURRENT_TIMESTAMP 和 ON UPDATE CURRENT_TIMESTAMP属性。
声明为NOT NULL且没有默认子句的TIMESTAMP列是没有默认值的。往数据表中插入列，又没有给TIMESTAMP列赋值时，如果是严格SQL模式，会抛出一个错误，如果严格SQL模式没有启用，该列会赋值为'0000-00-00 00:00:00′，同时出现一个警告。（这和MySQL处理其他时间类型数据一样，如DATETIME）
（参见：//www.gxlcms.com/article/71107.htm）

也就是 explicit_defaults_for_timestamp 关闭了 timestamp 类型字段锁拥有的一些会让人感到奇怪的默认行为，加入了该参数之后，如果还需要为 timestamp类型的字段指定默认行为，那么就需要显示的在创建表时显示的指定。explicit_defaults_for_timestamp 也就是这个意思：显示指定默认值为timestamp类型的字段。