MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數(shù)

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MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數(shù)

MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數(shù):安裝MySQL時(shí)，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(dǎo)讀MySQL5.6中的TIMESTAMP和explicit_defaults_for_timestamp參數(shù):安裝MySQL時(shí)，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(shí)，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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[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(kāi)始，timestamp 的默認(rèn)行為已經(jīng)是 deprecated 了。

在MySQL 5.6.6之前，TIMESTAMP的默認(rèn)行為：

TIMESTAMP列如果沒(méi)有明確聲明NULL屬性，默認(rèn)為NOT NULL。（而其他數(shù)據(jù)類(lèi)型，如果沒(méi)有顯示聲明為NOT NULL，則允許NULL值。）設(shè)置TIMESTAMP的列值為NULL，會(huì)自動(dòng)存儲(chǔ)為當(dāng)前timestamp。

表中的第一個(gè)TIMESTAMP列，如果沒(méi)有聲明NULL屬性、DEFAULT或者 ON UPDATE，會(huì)自動(dòng)分配 DEFAULT CURRENT_TIMESTAMP和ON UPDATE CURRENT_TIMESTAMP 屬性。

表中第二個(gè)TIMESTAMP列，如果沒(méi)有聲明為NULL或者DEFAULT子句，默認(rèn)自動(dòng)分配'0000-00-00 00:00:00′。插入行時(shí)沒(méi)有指明改列的值，該列默認(rèn)分配'0000-00-00 00:00:00′，且沒(méi)有警告。
要關(guān)閉警告，需要加入下面的參數(shù)：

explicit_defaults_for_timestamp=true

重啟MySQL后錯(cuò)誤消失，這時(shí)TIMESTAMP的行為如下：

TIMESTAMP如果沒(méi)有顯示聲明NOT NULL，是允許NULL值的，可以直接設(shè)置改列為NULL，而沒(méi)有默認(rèn)填充行為。
TIMESTAMP不會(huì)默認(rèn)分配DEFAULT CURRENT_TIMESTAMP 和 ON UPDATE CURRENT_TIMESTAMP屬性。
聲明為NOT NULL且沒(méi)有默認(rèn)子句的TIMESTAMP列是沒(méi)有默認(rèn)值的。往數(shù)據(jù)表中插入列，又沒(méi)有給TIMESTAMP列賦值時(shí)，如果是嚴(yán)格SQL模式，會(huì)拋出一個(gè)錯(cuò)誤，如果嚴(yán)格SQL模式?jīng)]有啟用，該列會(huì)賦值為'0000-00-00 00:00:00′，同時(shí)出現(xiàn)一個(gè)警告。（這和MySQL處理其他時(shí)間類(lèi)型數(shù)據(jù)一樣，如DATETIME）
（參見(jiàn)：//www.gxlcms.com/article/71107.htm）

也就是 explicit_defaults_for_timestamp 關(guān)閉了 timestamp 類(lèi)型字段鎖擁有的一些會(huì)讓人感到奇怪的默認(rèn)行為，加入了該參數(shù)之后，如果還需要為 timestamp類(lèi)型的字段指定默認(rèn)行為，那么就需要顯示的在創(chuàng)建表時(shí)顯示的指定。explicit_defaults_for_timestamp 也就是這個(gè)意思：顯示指定默認(rèn)值為timestamp類(lèi)型的字段。