Mysql创建语句中的数据类型包括时间类型,有一下几类：
| DATE
| TIME[(fsp)]
| TIMESTAMP[(fsp)]
| DATETIME[(fsp)]
| YEAR
这几个类型中，特别值得注意的是DATE,DATETIME,TIMESTAMP有什么区别？
DATE
mysql> select get_format(date,‘ISO‘); +------------------------+ | get_format(date,‘ISO‘) | +------------------------+ | %Y-%m-%d | +------------------------+ 1 row in set (0.00 sec)
DATETIME
mysql> select get_format(datetime,‘ISO‘); +----------------------------+ | get_format(datetime,‘ISO‘) | +----------------------------+ | %Y-%m-%d %H:%i:%s | +----------------------------+ 1 row in set (0.00 sec)
TIMESTAMP
mysql> select get_format(timestamp,‘ISO‘); +-----------------------------+ | get_format(timestamp,‘ISO‘) | +-----------------------------+ | %Y-%m-%d %H:%i:%s | +-----------------------------+ 1 row in set (0.00 sec)
TIME
mysql> select get_format(time,‘ISO‘); +------------------------+ | get_format(time,‘ISO‘) | +------------------------+ | %H:%i:%s | +------------------------+ 1 row in set (0.00 sec)
YEAR
mysql> select year(curdate()); +-----------------+ | year(curdate()) | +-----------------+ | 2015 | +-----------------+ 1 row in set (0.00 sec)
上述中用到的是format的定义可以再函数DATE_FORMAT(date,format)中找到对格式的定义：
%a |
Abbreviated weekday name (Sun..Sat) |
%b |
Abbreviated month name (Jan..Dec) |
%c |
Month, numeric (0..12) |
%D |
Day of the month with English suffix (0th, 1st, 2nd, 3rd, …) |
%d |
Day of the month, numeric (00..31) |
%e |
Day of the month, numeric (0..31) |
%f |
Microseconds (000000..999999) |
%H |
Hour (00..23) |
%h |
Hour (01..12) |
%I |
Hour (01..12) |
%i |
Minutes, numeric (00..59) |
%j |
Day of year (001..366) |
%k |
Hour (0..23) |
%l |
Hour (1..12) |
%M |
Month name (January..December) |
%m |
Month, numeric (00..12) |
%p |
AM or PM |
%r |
Time, 12-hour (hh:mm:ss followed by AM or PM) |
%S |
Seconds (00..59) |
%s |
Seconds (00..59) |
%T |
Time, 24-hour (hh:mm:ss) |
%U |
Week (00..53), whereSunday is the first day of the week; WEEK() mode 0 |
%u |
Week (00..53), whereMonday is the first day of the week; WEEK() mode 1 |
%V |
Week (01..53), whereSunday is the first day of the week; WEEK() mode 2; used with %X |
%v |
Week (01..53), whereMonday is the first day of the week; WEEK() mode 3; used with %x |
%W |
Weekday name (Sunday..Saturday) |
%w |
Day of the week (0=Sunday..6=Saturday) |
%X |
Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V |
%x |
Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v |
%Y |
Year, numeric, four digits |
%y |
Year, numeric (two digits) |
%% |
A literal “%” character |
% |
x, for any “x” not listedabove |
为什么需要了解这点，首先在创建时间类型的字段时，如果需要指定时间类型和默认值，那么类型和默认值得关系必须明确，在官网中提到以下内容：
The DEFAULT clause specifies a default value for a
column. With one exception, the default value must be a constant; it cannot be a
function or an expression. This means, for example, that you cannot set the
default for a date column to be the value of a function such as NOW() or CURRENT_DATE. The exception is that you can specify CURRENT_TIMESTAMP as the default for a TIMESTAMP or (as of MySQL
5.6.5) DATETIME column. See Section 11.3.5, “Automatic Initialization
and Updating for TIMESTAMP and DATETIME”.
简单的说就是默认值必须是常量，不允许使用时间函数，只能使用CURRENT_TIMESTAMP作为TIMESTAMP和DATETIME类型的默认值。比如指定了默认值，那么当使用DATE类型时会明显的出现如下错误警告：
[Err] 1067 - Invalid default value for ‘ACT_DATE‘
正确的创建默认时间只能如下：
CREATE TABLE ACT_TAB ( ACT_TIME TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, ACT_DATE DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP );
参照：
http://dev.mysql.com/doc/refman/5.6/en/date-and-time-functions.html#function_get-format
http://dev.mysql.com/doc/refman/5.6/en/create-table.html
http://dev.mysql.com/doc/refman/5.6/en/timestamp-initialization.html