MySQL time date types and related functions
1. Date type
Date and time types in MySQL| Types of | byte | minimum | maximum value | zero value |
| DATETIME | 8 | 1000-01-01 00:00:00 | 9999-12-31 23:59:59 | 0000-00-00 00:00:00 |
| DATE | 4 | 1000-01-01 | 9999-12-31 | 0000-00-00 |
| TIMESTAMP | 4 | 19700101080001 | sometime in 2038 | 00000000000000 |
| TIME | 3 | -838:59:59 | 838:59:59 | 00:00:00 |
| YEAR | 1 | 1901 | 2155 | 0000 |
The format returned by TIMESTAMP is "YYYY-MM-DD HH:MM:SS", and the width is fixed to 19 characters. To get the numeric value, you can select the current_timestamp+0 method:
YEAR has year in 2-digit (version before 5.5.27) or 4-digit format, the default is 4-digit format, in 4-digit format, allowed values are 1901 ~ 2155 and 0000, in 2-digit format, allowed values It is 70 ~ 69, which means 1970 ~ 2069, and the format returned by YEAR is "YYYY".
For all the above time and date types, if you want to insert the value corresponding to the current time, you can use current_timestamp, now():
Second, time and date functions
Datetime functions in MySQL
| function | Function | Format |
| CURDATE () | Returns the current date | 2016-10-29 |
| LIKE() | return current time | 11:20:34 |
| NOW() | Returns the current date and time | 2016-10-29 11:21:02 |
| UNIX_TIMESTAMP(date) UNIX_TIMESTAMP() |
Returns the UNIX timestamp of the date date | Execute: select unix_timestamp() Output: 1477711822 |
| FROM_UNIXTIME(unix_timestamp) | Returns the date value of a UNIX timestamp | Execute: select from_unixtime(1477670400) Output: 2016-10-29 11:30:22 |
| WEEK(date) | Returns date as the week of the year | Execute: select week(curdate()) output: 43 |
| YEAR(date) | Returns the year of the date date | Execute: select year(curdate()) Output: 2016 |
| HOUR(time) | Returns the hour value of time | Execute: select hour(curtime()); output: 11 |
| MINUTE(time) | Returns the minute value of time | Execute: select minute(curtime()) Output: 36 |
| MONTHNAME(date) | Returns the month name of date | Execute: select monthname(curdate()) outputOctober |
| DATE_FORMAT(date, format) | Returns the date value formatted in string format | Execution: select date_format(now(), '%Y year %c month %e day %T hour %i minute %S second'); Output: Oct 29, 2016 11:44:57:44:57 |
| DATE_ADD(date,INTERVAL expr type) | Returns a date value plus the time value of a time interval | 执行：select now() current,date_add(now(),INTERVAL 1 day) after_one_day; Output: 2016-10-29 11:52:10 | 2016-10-30 11:52:10 |
| DATEDIFF(expr1,expr2) | Returns the number of days between start time expr1 and end time expr2 | Execute: select datediff('2016-10-20',now()); output: -9 Execute: select datediff(now(),'2016-10-20') output: 9 |
UNIX_TIMESTAMP(date) and FROM_UNIXTIME(unix_timestamp) are reciprocal.
DATE_FORMAT(date,format) function:
Format character in format string:
Date and time formats in MySQL| format character | format description |
| %S and %s | Seconds as two digits (00, 01, ... , 59) |
| %i | Two-digit minute (00, 01, ... , 59) |
| %H | Two-digit hour, 24 hours (00,01,...,23) |
| % h sum% I |
Two-digit hour, 24 hours (01,02,...,12) |
| %k | Hours as numbers, 24 hours (0,1,2,...,23) |
| %l | Hours in numeric form, 12 hours (1,2,...,12) |
| %T | 24-hour time format (hh:mm:ss) |
| %r | 12-hour time format (hh:mm:ssAM or hh:mm:ssPM) |
| %p | AM or PM |
| %W | The name of each day of the week (Sunday,Monday,...,Saturday) |
| %a | Abbreviated names for each day of the week (Sun,Mon,...,Sat) |
| %d | Two digits representing the day of the month (00,01,...,31) |
| %e | The number represents the day of the month (1,2,...,31) |
| %D | The English suffix indicates the number of days in the month (1st, 2nd, 3rd,...) |
| %w | Number of days of the week (0=Sunday, 1=Monday...) |
| %j | Day of the year as 3 digits (001,002,...,366) |
| % U | Week of the year (0,1...,52), where Sunday is the first day of the week |
| % u | Week of the year (0,1...,52), where Monday is the first day of the week |
| %M | Month name (January,February,...,December) |
| %b | Abbreviated month names (Jan,Feb,...Dec) |
| %m | Two-digit month (01,02,...,12) |
| %c | Number of months (1,2,...,12) |
| %AND | 4-digit year |
| %and | year in two digits |
| %% | escape |
Example:
DATE_ADD(date,INTERVAL expr type): The INTERVAL time interval type keyword, expr is an expression, corresponding to the following type, type time interval type, its value is as follows
MySQL date interval type| expression type | describe | Format |
| HOUR | Hour | hh |
| MINUTE | Minute | mm |
| SECOND | Second | ss |
| YEAR | year | YY |
| MONTH |
moon | MM |
| DAY | day | DD |
| YEAR_MONTH | year and month | YY-MM |
| DAY_HOUR | day and hour | DD hh |
| DAY_MINUTE | 日和分钟 | DD hh:mm |
| DAY_SECOND | 日和秒 | DD hh:mm:ss |
| HOUR_MINUTE | 小时和分 | hh:mm |
| HOUR_SECOND | 小时和秒 | hh:ss |
| MINUTE_SECOND | 分钟和秒 | mm:ss |
例如，得到3天5小时后的时间：
得到3天5小时前的时间：
关于datetime和timestamp
MySQL中datetime能保存的日期范围从1001年到9999年，精度为秒，存储时把日期和时间封装为YYYYMMDDHHMMSS的格式的整数中，与时区无关，使用8个字节存储。
timestamp类型能保存的日期范围从1970年1月1日到2038年12月31日，它存储的是时间戳，只用了4个字节，所以范围比datetime小很多，timestamp是和时区相关的。默认情况下，如果插入时没有指定第一个timestamp列的值，那么mysql会默认给设置当前时间。在更新一行记录时，也会更新第一个timestamp列的值为当前时间（除非指定了该列的值）