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MySQL datediff(date1,date2)：兩個(gè)日期相減 date1 - date2，返回天數(shù)。select datediff('2008-08-08', '2008-08-01'); -- 7select datediff('2008-08-01', '2008-08-08'); -- -7一、MySQL 獲得當(dāng)前日期時(shí)間 函數(shù)1.1 獲得當(dāng)前日期+時(shí)間（date + time）函數(shù)：now()mysql> select now();+---------------------+| now()               |+---------------------+| 2008-08-08 22:20:46 |+---------------------+除了 now() 函數(shù)能獲得當(dāng)前的日期時(shí)間外，MySQL 中還有下面的函數(shù)： current_timestamp(),current_timestamp,localtime(),localtime,localtimestamp    -- (v4.0.6),localtimestamp()  -- (v4.0.6)這些日期時(shí)間函數(shù)，都等同于 now()。鑒于 now() 函數(shù)簡(jiǎn)短易記，建議總是使用 now() 來(lái)替代上面列出的函數(shù)。1.2 獲得當(dāng)前日期+時(shí)間（date + time）函數(shù)：sysdate()sysdate() 日期時(shí)間函數(shù)跟 now() 類(lèi)似，不同之處在于：now() 在執(zhí)行開(kāi)始時(shí)值就得到了， sysdate() 在函數(shù)執(zhí)行時(shí)動(dòng)態(tài)得到值。看下面的例子就明白了：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 |+---------------------+----------+---------------------+可以看到，雖然中途 sleep 3 秒，但 now() 函數(shù)兩次的時(shí)間值是相同的； sysdate() 函數(shù)兩次得到的時(shí)間值相差 3 秒。MySQL Manual 中是這樣描述 sysdate() 的：Return the time at which the function executes。sysdate() 日期時(shí)間函數(shù)，一般情況下很少用到。2. 獲得當(dāng)前日期（date）函數(shù)：curdate()mysql> select curdate();+------------+| curdate()  |+------------+| 2008-08-08 |+------------+其中，下面的兩個(gè)日期函數(shù)等同于 curdate()： current_date(),current_date3. 獲得當(dāng)前時(shí)間（time）函數(shù)：curtime()mysql> select curtime();+-----------+| curtime() |+-----------+| 22:41:30  |+-----------+其中，下面的兩個(gè)時(shí)間函數(shù)等同于 curtime()： current_time(),current_time4. 獲得當(dāng)前 UTC 日期時(shí)間函數(shù)：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 |+---------------------+------------+------------+---------------------+因?yàn)槲覈?guó)位于東八時(shí)區(qū)，所以本地時(shí)間 = UTC 時(shí)間 + 8 小時(shí)。UTC 時(shí)間在業(yè)務(wù)涉及多個(gè)國(guó)家和地區(qū)的時(shí)候，非常有用。二、MySQL 日期時(shí)間 Extract（選取） 函數(shù)。1. 選取日期時(shí)間的各個(gè)部分：日期、時(shí)間、年、季度、月、日、小時(shí)、分鐘、秒、微秒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); -- 1234562. MySQL Extract() 函數(shù)，可以上面實(shí)現(xiàn)類(lèi)似的功能：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); -- 123456select 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); --        30123456MySQL Extract() 函數(shù)除了沒(méi)有date(),time() 的功能外，其他功能一應(yīng)具全。并且還具有選取‘day_microsecond’ 等功能。注意這里不是只選取 day 和 microsecond，而是從日期的 day 部分一直選取到 microsecond 部分。夠強(qiáng)悍的吧！MySQL Extract() 函數(shù)唯一不好的地方在于：你需要多敲幾次鍵盤(pán)。3. MySQL dayof... 函數(shù)：dayofweek(), dayofmonth(), dayofyear()分別返回日期參數(shù)，在一周、一月、一年中的位置。set @dt = '2008-08-08';select dayofweek(@dt);   -- 6select dayofmonth(@dt);  -- 8select dayofyear(@dt);   -- 221日期 '2008-08-08' 是一周中的第 6 天（1 = Sunday, 2 = Monday, ..., 7 = Saturday）；一月中的第 8 天；一年中的第 221 天。4. MySQL week... 函數(shù)：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);    -- 200831MySQL week() 函數(shù)，可以有兩個(gè)參數(shù)，具體可看手冊(cè)。 weekofyear() 和 week() 一樣，都是計(jì)算“某天”是位于一年中的第幾周。 weekofyear(@dt) 等價(jià)于 week(@dt,3)。MySQL weekday() 函數(shù)和 dayofweek() 類(lèi)似，都是返回“某天”在一周中的位置。不同點(diǎn)在于參考的標(biāo)準(zhǔn)， weekday：(0 = Monday, 1 = Tuesday, ..., 6 = Sunday)； dayofweek：（1 = Sunday, 2 = Monday, ..., 7 = Saturday）MySQL yearweek() 函數(shù)，返回 year(2008) + week 位置(31)。5. MySQL 返回星期和月份名稱(chēng)函數(shù)：dayname(), monthname()set @dt = '2008-08-08';select dayname(@dt);     -- Fridayselect monthname(@dt);   -- August思考，如何返回中文的名稱(chēng)呢？6. MySQL last_day() 函數(shù)：返回月份中的最后一天。select last_day('2008-02-01');  -- 2008-02-29select last_day('2008-08-08');  -- 2008-08-31MySQL last_day() 函數(shù)非常有用，比如我想得到當(dāng)前月份中有多少天，可以這樣來(lái)計(jì)算：mysql> select now(), day(last_day(now())) as days;+---------------------+------+| now()               | days |+---------------------+------+| 2008-08-09 11:45:45 |   31 |+---------------------+------+三、MySQL 日期時(shí)間計(jì)算函數(shù)1. MySQL 為日期增加一個(gè)時(shí)間間隔：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 dayMySQL adddate(), addtime()函數(shù)，可以用 date_add() 來(lái)替代。下面是 date_add() 實(shí)現(xiàn) addtime() 功能示例：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                             |+-------------------------------------------------+date_add() 函數(shù)，分別為 @dt 增加了“1小時(shí) 15分 30秒” 和 “1天 1小時(shí) 15分 30秒”。建議：總是使用 date_add() 日期時(shí)間函數(shù)來(lái)替代 adddate(), addtime()。2. MySQL 為日期減去一個(gè)時(shí)間間隔：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                                            |+----------------------------------------------------------------+MySQL date_sub() 日期時(shí)間函數(shù) 和 date_add() 用法一致，不再贅述。另外，MySQL 中還有兩個(gè)函數(shù) subdate(), subtime()，建議，用 date_sub() 來(lái)替代。3. MySQL 另類(lèi)日期函數(shù)：period_add(P,N), period_diff(P1,P2)函數(shù)參數(shù)“P” 的格式為“YYYYMM” 或者 “YYMM”，第二個(gè)參數(shù)“N” 表示增加或減去 N month（月）。MySQL period_add(P,N)：日期加/減去N月。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)：日期 P1-P2，返回 N 個(gè)月。mysql> select period_diff(200808, 200801);+-----------------------------+| period_diff(200808, 200801) |+-----------------------------+|                           7 |+-----------------------------+在 MySQL 中，這兩個(gè)日期函數(shù)，一般情況下很少用到。4. MySQL 日期、時(shí)間相減函數(shù)：datediff(date1,date2), timediff(time1,time2)MySQL datediff(date1,date2)：兩個(gè)日期相減 date1 - date2，返回天數(shù)。select datediff('2008-08-08', '2008-08-01');  -- 7select datediff('2008-08-01', '2008-08-08');  -- -7MySQL timediff(time1,time2)：兩個(gè)日期相減 time1 - time2，返回 time 差值。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注意：timediff(time1,time2) 函數(shù)的兩個(gè)參數(shù)類(lèi)型必須相同。四、MySQL 日期轉(zhuǎn)換函數(shù)、時(shí)間轉(zhuǎn)換函數(shù)1. MySQL （時(shí)間、秒）轉(zhuǎn)換函數(shù)：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 （日期、天數(shù)）轉(zhuǎn)換函數(shù)：to_days(date), from_days(days)select to_days('0000-00-00');  -- 0select to_days('2008-08-08');  -- 733627select from_days(0);           -- '0000-00-00'select from_days(733627);      -- '2008-08-08'3. MySQL Str to Date （字符串轉(zhuǎn)換為日期）函數(shù)：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可以看到，str_to_date(str,format) 轉(zhuǎn)換函數(shù)，可以把一些雜亂無(wú)章的字符串轉(zhuǎn)換為日期格式。另外，它也可以轉(zhuǎn)換為時(shí)間。“format” 可以參看 MySQL 手冊(cè)。4. MySQL Date/Time to Str（日期/時(shí)間轉(zhuǎn)換為字符串）函數(shù)：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 日期、時(shí)間轉(zhuǎn)換函數(shù)：date_format(date,format), time_format(time,format) 能夠把一個(gè)日期/時(shí)間轉(zhuǎn)換成各種各樣的字符串格式。它是 str_to_date(str,format) 函數(shù)的 一個(gè)逆轉(zhuǎn)換。5. MySQL 獲得國(guó)家地區(qū)時(shí)間格式函數(shù)：get_format()MySQL get_format() 語(yǔ)法：get_format(date|time|datetime, 'eur'|'usa'|'jis'|'iso'|'internal'MySQL get_format() 用法的全部示例：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'MySQL get_format() 函數(shù)在實(shí)際中用到機(jī)會(huì)的比較少。6. MySQL 拼湊日期、時(shí)間函數(shù)：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);  -- '12:15:30'五、MySQL 時(shí)間戳（Timestamp）函數(shù)1. MySQL 獲得當(dāng)前時(shí)間戳函數(shù)：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 時(shí)間戳、日期）轉(zhuǎn)換函數(shù)：unix_timestamp(),unix_timestamp(date),from_unixtime(unix_timestamp),from_unixtime(unix_timestamp,format)下面是示例：select unix_timestamp();                       -- 1218290027select unix_timestamp('2008-08-08');           -- 1218124800select unix_timestamp('2008-08-08 12:30:00');  -- 1218169800select 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 時(shí)間戳（timestamp）轉(zhuǎn)換、增、減函數(shù)：timestamp(date)                                     -- date to timestamptimestamp(dt,time)                                  -- dt + timetimestampadd(unit,interval,datetime_exPR)           --timestampdiff(unit,datetime_expr1,datetime_expr2)   --請(qǐng)看示例部分：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 09:01:01select 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 08:00:00MySQL timestampadd() 函數(shù)類(lèi)似于 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');           -- 7MySQL timestampdiff() 函數(shù)就比 datediff() 功能強(qiáng)多了，datediff() 只能計(jì)算兩個(gè)日期（date）之間相差的天數(shù)。六、MySQL 時(shí)區(qū)（timezone）轉(zhuǎn)換函數(shù)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時(shí)區(qū)轉(zhuǎn)換也可以通過(guò) date_add, date_sub, timestampadd 來(lái)實(shí)現(xiàn)。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