MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數

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MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數

MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數:安裝MySQL時，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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導讀MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數:安裝MySQL時，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

安裝MySQL時，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

To start mysqld at boot time you have to copy
support-files/mysql.server to the right place for your system

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

 ./bin/mysqladmin -u root password 'new-password'
 ./bin/mysqladmin -u root -h localhost.localdomain password 'new-password'

Alternatively you can run:

 ./bin/mysql_secure_installation

which will also give you the option of removing the test
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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
If you do not want to use this, either remove it, or use the
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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).

其原因是從 5.6開始，timestamp 的默認行為已經是 deprecated 了。

在MySQL 5.6.6之前，TIMESTAMP的默認行為：

TIMESTAMP列如果沒有明確聲明NULL屬性，默認為NOT NULL。（而其他數據類型，如果沒有顯示聲明為NOT NULL，則允許NULL值。）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，如果沒有聲明NULL屬性、DEFAULT或者 ON UPDATE，會自動分配 DEFAULT CURRENT_TIMESTAMP和ON UPDATE CURRENT_TIMESTAMP 屬性。

表中第二個TIMESTAMP列，如果沒有聲明為NULL或者DEFAULT子句，默認自動分配'0000-00-00 00:00:00′。插入行時沒有指明改列的值，該列默認分配'0000-00-00 00:00:00′，且沒有警告。
要關閉警告，需要加入下面的參數：

explicit_defaults_for_timestamp=true

重啟MySQL后錯誤消失，這時TIMESTAMP的行為如下：

TIMESTAMP如果沒有顯示聲明NOT NULL，是允許NULL值的，可以直接設置改列為NULL，而沒有默認填充行為。
TIMESTAMP不會默認分配DEFAULT CURRENT_TIMESTAMP 和 ON UPDATE CURRENT_TIMESTAMP屬性。
聲明為NOT NULL且沒有默認子句的TIMESTAMP列是沒有默認值的。往數據表中插入列，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處理其他時間類型數據一樣，如DATETIME）
（參見：//www.gxlcms.com/article/71107.htm）

也就是 explicit_defaults_for_timestamp 關閉了 timestamp 類型字段鎖擁有的一些會讓人感到奇怪的默認行為，加入了該參數之后，如果還需要為 timestamp類型的字段指定默認行為，那么就需要顯示的在創建表時顯示的指定。explicit_defaults_for_timestamp 也就是這個意思：顯示指定默認值為timestamp類型的字段。