MySQL: Summary of date and time functions _ MySQL

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1. MySQL obtains the current date and time function

1.1 obtain the current date + time (date + time) function: now ()

mysql> select now();+---------------------+| now()               |+---------------------+| 2008-08-08 22:20:46 |+---------------------+

In addition to the now () function, MySQL also has the following functions:

 current_timestamp(),current_timestamp,localtime(),localtime,localtimestamp    -- (v4.0.6),localtimestamp()  -- (v4.0.6)

These datetime functions are equivalent to now (). Considering that the now () function is short and easy to remember, we recommend that you always use now () to replace the functions listed above.

1.2 obtain the current date + time (date + time) function: sysdate ()

The sysdate () date and time function is similar to now (). The difference is that now () is obtained at the execution start time, and sysdate () dynamically obtains the value during function execution. You can see the following example:

mysql> select now(), sleep(3), now();+---------------------+----------+---------------------+| now()               | sleep(3) | now()               |+---------------------+----------+---------------------+| 2008-08-08 22:28:21 |        0 | 2008-08-08 22:28:21 |+---------------------+----------+---------------------+

mysql> select sysdate(), sleep(3), sysdate();+---------------------+----------+---------------------+| sysdate()           | sleep(3) | sysdate()           |+---------------------+----------+---------------------+| 2008-08-08 22:28:41 |        0 | 2008-08-08 22:28:44 |+---------------------+----------+---------------------+

We can see that although sleep lasts for 3 seconds, the time values of the now () function are the same. the time values obtained by The sysdate () function differ by 3 seconds. In MySQL Manual, sysdate () is described as follows: Return the time at which the function executes.

Sysdate () date and time functions are rarely used.

2. obtain the current date function: curdate ()

mysql> select curdate();+------------+| curdate()  |+------------+| 2008-08-08 |+------------+

The following two date functions are equivalent to curdate ():

 current_date(),current_date

3. obtain the current time function: curtime ()

mysql> select curtime();+-----------+| curtime() |+-----------+| 22:41:30  |+-----------+

The following two time functions are equivalent to curtime ():

 current_time(),current_time

4. obtain the current UTC date and time functions: utc_date (), utc_time (), utc_timestamp ()

mysql> select utc_timestamp(), utc_date(), utc_time(), now()+---------------------+------------+------------+---------------------+| utc_timestamp()     | utc_date() | utc_time() | now()               |+---------------------+------------+------------+---------------------+| 2008-08-08 14:47:11 | 2008-08-08 | 14:47:11   | 2008-08-08 22:47:11 |+---------------------+------------+------------+---------------------+

Because our country is located in the East eight time zone, the local time = UTC time + 8 hours. UTC time is very useful when your business involves multiple countries and regions.

II. MySQL date and time Extract (select) function.

1. select each part of the date and time: date, time, year, quarter, month, day, hour, minute, second, microsecond

set @dt = '2008-09-10 07:15:30.123456';select date(@dt);        -- 2008-09-10select time(@dt);        -- 07:15:30.123456select year(@dt);        -- 2008select quarter(@dt);     -- 3select month(@dt);       -- 9select week(@dt);        -- 36select day(@dt);         -- 10select hour(@dt);        -- 7select minute(@dt);      -- 15select second(@dt);      -- 30select microsecond(@dt); -- 123456

2. MySQL Extract () function, which can implement similar functions:

set @dt = '2008-09-10 07:15:30.123456';select extract(year                from @dt); -- 2008select extract(quarter             from @dt); -- 3select extract(month               from @dt); -- 9select extract(week                from @dt); -- 36select extract(day                 from @dt); -- 10select extract(hour                from @dt); -- 7select extract(minute              from @dt); -- 15select extract(second              from @dt); -- 30select extract(microsecond         from @dt); -- 123456

select extract(year_month          from @dt); -- 200809select extract(day_hour            from @dt); -- 1007select extract(day_minute          from @dt); -- 100715select extract(day_second          from @dt); -- 10071530select extract(day_microsecond     from @dt); -- 10071530123456select extract(hour_minute         from @dt); --    715select extract(hour_second         from @dt); --    71530select extract(hour_microsecond    from @dt); --    71530123456select extract(minute_second       from @dt); --      1530select extract(minute_microsecond  from @dt); --      1530123456select extract(second_microsecond  from @dt); --        30123456

In addition to date () and time () functions, the MySQL Extract () function must be fully functional. You can also select 'Day _ microsecond. Note that we will not only select day and microsecond, but choose from day of the date to microsecond. Powerful enough!

The only bad thing about the MySQL Extract () function is that you need to press the keyboard several more times.

3. MySQL dayof... function: dayofweek (), dayofmonth (), dayofyear ()

Return the date parameters in the range of one week, one month, and one year.

set @dt = '2008-08-08';select dayofweek(@dt);   -- 6select dayofmonth(@dt);  -- 8select dayofyear(@dt);   -- 221

The date '2017-08-08 'is the first day of the week (1 = Sunday, 2 = Monday,..., 7 = Saturday); the second day of the month; the second day of the year.

4. MySQL week... function: week (), weekofyear (), dayofweek (), weekday (), yearweek ()

set @dt = '2008-08-08';select week(@dt);        -- 31select week(@dt,3);      -- 32select weekofyear(@dt);  -- 32select dayofweek(@dt);   -- 6select weekday(@dt);     -- 4select yearweek(@dt);    -- 200831

The MySQL week () function has two parameters. for details, refer to the manual. Similar to weekofyear () and week (), weekofyear is the day of the year in which the calculation "one day" is located. Weekofyear (@ dt) is equivalent to week (@ dt, 3 ).

The MySQL weekday () function is similar to dayofweek () and returns the position of "one day" in a week. The difference lies in the reference standard, weekday :( 0 = Monday, 1 = Tuesday ,..., 6 = Sunday); dayofweek :( 1 = Sunday, 2 = Monday ,..., 7 = Saturday)

MySQL yearweek () function, returns year (2008) + week position (31 ).

5. MySQL returns the week and month name functions: dayname (), monthname ()

set @dt = '2008-08-08';select dayname(@dt);     -- Fridayselect monthname(@dt);   -- August

Think about how to return the Chinese name?

6. MySQL last_day () function: returns the last day of the month.

select last_day('2008-02-01');  -- 2008-02-29select last_day('2008-08-08');  -- 2008-08-31

The MySQL last_day () function is very useful. for example, you can calculate the number of days in the current month as follows:

mysql> select now(), day(last_day(now())) as days;+---------------------+------+| now()               | days |+---------------------+------+| 2008-08-09 11:45:45 |   31 |+---------------------+------+

III. MySQL date and time calculation functions

1. MySQL adds a time interval for the date: date_add ()

set @dt = now();select date_add(@dt, interval 1 day);        -- add 1 dayselect date_add(@dt, interval 1 hour);       -- add 1 hourselect date_add(@dt, interval 1 minute);     -- ...select date_add(@dt, interval 1 second);select date_add(@dt, interval 1 microsecond);select date_add(@dt, interval 1 week);select date_add(@dt, interval 1 month);select date_add(@dt, interval 1 quarter);select date_add(@dt, interval 1 year);

select date_add(@dt, interval -1 day);       -- sub 1 day

MySQL adddate () and addtime () functions can be replaced by date_add. The following is an example of addtime () implemented by date_add:

mysql> set @dt = '2008-08-09 12:12:33';mysql>mysql> select date_add(@dt, interval '01:15:30' hour_second);+------------------------------------------------+| date_add(@dt, interval '01:15:30' hour_second) |+------------------------------------------------+| 2008-08-09 13:28:03                            |+------------------------------------------------+

mysql> select date_add(@dt, interval '1 01:15:30' day_second);+-------------------------------------------------+| date_add(@dt, interval '1 01:15:30' day_second) |+-------------------------------------------------+| 2008-08-10 13:28:03                             |+-------------------------------------------------+

The date_add () function adds "1 hour 15 minutes 30 seconds" and "1 day 1 hour 15 minutes 30 seconds" to @ dt respectively ". Suggestion: Always use the date_add () date and time function to replace adddate () and addtime ().

2. MySQL is a date minus a time interval: date_sub ()

mysql> select date_sub('1998-01-01 00:00:00', interval '1 1:1:1' day_second);+----------------------------------------------------------------+| date_sub('1998-01-01 00:00:00', interval '1 1:1:1' day_second) |+----------------------------------------------------------------+| 1997-12-30 22:58:59                                            |+----------------------------------------------------------------+

The usage of MySQL date_sub () DATETIME function is the same as that of date_add. In addition, there are two subdate () and subtime () functions in MySQL. we recommend that you use date_sub () instead.

3. MySQL alternative date functions: period_add (P, N), period_diff (P1, P2)

The format of the function parameter "P" is "YYYYMM" or "YYMM". The second parameter "N" indicates adding or subtracting N month ).

MySQL period_add (P, N): date plus/minus N months.

mysql> select period_add(200808,2), period_add(20080808,-2)+----------------------+-------------------------+| period_add(200808,2) | period_add(20080808,-2) |+----------------------+-------------------------+|               200810 |                20080806 |+----------------------+-------------------------+

MySQL period_diff (P1, P2): date P1-P2, returns N months.

mysql> select period_diff(200808, 200801);+-----------------------------+| period_diff(200808, 200801) |+-----------------------------+|                           7 |+-----------------------------+

In MySQL, these two date functions are rarely used.

4. MySQL date and time subtraction functions: datediff (date1, date2), timediff (time1, time2)

MySQL datediff (date1, date2): two dates subtract date1-date2 and return the number of days.

select datediff('2008-08-08', '2008-08-01');  -- 7select datediff('2008-08-01', '2008-08-08');  -- -7

MySQL timediff (time1, time2): two dates minus time1-time2, return the time difference.

select timediff('2008-08-08 08:08:08', '2008-08-08 00:00:00'); -- 08:08:08select timediff('08:08:08', '00:00:00');                       -- 08:08:08

Note: the two parameter types of the timediff (time1, time2) function must be the same.

IV. MySQL date conversion function and time conversion function

1. MySQL (time, second) conversion function: time_to_sec (time), sec_to_time (seconds)

select time_to_sec('01:00:05');  -- 3605select sec_to_time(3605);        -- '01:00:05'

2. MySQL (date, number of days) conversion functions: to_days (date), from_days (days)

select to_days('0000-00-00');  -- 0select to_days('2008-08-08');  -- 733627

select from_days(0);           -- '0000-00-00'select from_days(733627);      -- '2008-08-08'

3. MySQL Str to Date (string converted to Date) function: str_to_date (str, format)

select str_to_date('08/09/2008', '%m/%d/%Y');                   -- 2008-08-09select str_to_date('08/09/08'  , '%m/%d/%y');                   -- 2008-08-09select str_to_date('08.09.2008', '%m.%d.%Y');                   -- 2008-08-09select str_to_date('08:09:30', '%h:%i:%s');                     -- 08:09:30select str_to_date('08.09.2008 08:09:30', '%m.%d.%Y %h:%i:%s'); -- 2008-08-09 08:09:30

We can see that the str_to_date (str, format) conversion function can convert disordered strings into date formats. In addition, it can be converted to time. For "format", see the MySQL manual.

4. MySQL Date/Time to Str (convert date/time to string) functions: date_format (Date, format), time_format (Time, format)

mysql> select date_format('2008-08-08 22:23:00', '%W %M %Y');+------------------------------------------------+| date_format('2008-08-08 22:23:00', '%W %M %Y') |+------------------------------------------------+| Friday August 2008                             |+------------------------------------------------+

mysql> select date_format('2008-08-08 22:23:01', '%Y%m%d%H%i%s');+----------------------------------------------------+| date_format('2008-08-08 22:23:01', '%Y%m%d%H%i%s') |+----------------------------------------------------+| 20080808222301                                     |+----------------------------------------------------+

mysql> select time_format('22:23:01', '%H.%i.%s');+-------------------------------------+| time_format('22:23:01', '%H.%i.%s') |+-------------------------------------+| 22.23.01                            |+-------------------------------------+

MySQL date and time conversion functions: date_format (date, format), time_format (time, format) can convert a date/time to a variety of string formats. It is an inverse conversion of the str_to_date (str, format) function.

5. MySQL returns the country/region time format function: get_format ()

MySQL get_format () syntax:

get_format(date|time|datetime, 'eur'|'usa'|'jis'|'iso'|'internal'

All examples of MySQL get_format () usage:

select get_format(date,'usa')          ;   -- '%m.%d.%Y'select get_format(date,'jis')          ;   -- '%Y-%m-%d'select get_format(date,'iso')          ;   -- '%Y-%m-%d'select get_format(date,'eur')          ;   -- '%d.%m.%Y'select get_format(date,'internal')     ;   -- '%Y%m%d'select get_format(datetime,'usa')      ;   -- '%Y-%m-%d %H.%i.%s'select get_format(datetime,'jis')      ;   -- '%Y-%m-%d %H:%i:%s'select get_format(datetime,'iso')      ;   -- '%Y-%m-%d %H:%i:%s'select get_format(datetime,'eur')      ;   -- '%Y-%m-%d %H.%i.%s'select get_format(datetime,'internal') ;   -- '%Y%m%d%H%i%s'select get_format(time,'usa')          ;   -- '%h:%i:%s %p'select get_format(time,'jis')          ;   -- '%H:%i:%s'select get_format(time,'iso')          ;   -- '%H:%i:%s'select get_format(time,'eur')          ;   -- '%H.%i.%s'select get_format(time,'internal')     ;   -- '%H%i%s'

The MySQL get_format () function has fewer opportunities in practice.

6. MySQL patchwork date and time functions: makdedate (year, dayofyear), maketime (hour, minute, second)

select makedate(2001,31);   -- '2001-01-31'select makedate(2001,32);   -- '2001-02-01'

select maketime(12,15,30);  -- '12:15:30'

V. MySQL Timestamp function

1. MySQL returns the current timestamp function: current_timestamp, current_timestamp ()

mysql> select current_timestamp, current_timestamp();+---------------------+---------------------+| current_timestamp   | current_timestamp() |+---------------------+---------------------+| 2008-08-09 23:22:24 | 2008-08-09 23:22:24 |+---------------------+---------------------+

2. MySQL (Unix timestamp, date) conversion function:

unix_timestamp(),unix_timestamp(date),from_unixtime(unix_timestamp),from_unixtime(unix_timestamp,format)

The following is an example:

select unix_timestamp();                       -- 1218290027select unix_timestamp('2008-08-08');           -- 1218124800select unix_timestamp('2008-08-08 12:30:00');  -- 1218169800

select from_unixtime(1218290027);              -- '2008-08-09 21:53:47'select from_unixtime(1218124800);              -- '2008-08-08 00:00:00'select from_unixtime(1218169800);              -- '2008-08-08 12:30:00'

select from_unixtime(1218169800, '%Y %D %M %h:%i:%s %x'); -- '2008 8th August 12:30:00 2008'

3. MySQL timestamp conversion, addition, and subtraction functions:

timestamp(date)                                     -- date to timestamptimestamp(dt,time)                                  -- dt + timetimestampadd(unit,interval,datetime_expr)           --timestampdiff(unit,datetime_expr1,datetime_expr2)   --

See the example section:

select timestamp('2008-08-08');                         -- 2008-08-08 00:00:00select timestamp('2008-08-08 08:00:00', '01:01:01');    -- 2008-08-08 09:01:01select timestamp('2008-08-08 08:00:00', '10 01:01:01'); -- 2008-08-18 09:01:01

select timestampadd(day, 1, '2008-08-08 08:00:00');     -- 2008-08-09 08:00:00select date_add('2008-08-08 08:00:00', interval 1 day); -- 2008-08-09 08:00:00

The MySQL timestampadd () function is similar to date_add ().

select timestampdiff(year,'2002-05-01','2001-01-01');                    -- -1select timestampdiff(day ,'2002-05-01','2001-01-01');                    -- -485select timestampdiff(hour,'2008-08-08 12:00:00','2008-08-08 00:00:00');  -- -12select datediff('2008-08-08 12:00:00', '2008-08-01 00:00:00');           -- 7

MySQL timestampdiff () functions are much more powerful than datediff () functions. datediff () can only calculate the number of days for the difference between two dates.

VI. MySQL timezone conversion function

convert_tz(dt,from_tz,to_tz)

select convert_tz('2008-08-08 12:00:00', '+08:00', '+00:00'); -- 2008-08-08 04:00:00

You can also use date_add, date_sub, and timestampadd to convert time zones.

select date_add('2008-08-08 12:00:00', interval -8 hour);  -- 2008-08-08 04:00:00select date_sub('2008-08-08 12:00:00', interval  8 hour);  -- 2008-08-08 04:00:00select timestampadd(hour, -8, '2008-08-08 12:00:00');      -- 2008-08-08 04:00:00

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