最近蒐集了一下網上關於mysql的日期/時間函式的介紹，整理後自己進行了一些小實驗

一、 Mysql獲得當前日期時間

Now(): 獲得當前的日期+時間（date + time）函式：
mysql> select now();
+---------------------+
| now()             |
+---------------------+
| 2011-03-01 10:26:23 |
+---------------------+
1 row in set (0.00 sec)
同等的函式還包括current_timestamp(),localtime()，但是now()最容易記憶，所以推薦使用。

Sysdate(): 日期時間函式跟 now() 類似，不同之處在於：now() 在執行開始時值就得到了， sysdate() 在函式執行時動態得到值。
看下面的例子就明白了：
mysql> select now(),sleep(3),now();
+---------------------+----------+---------------------+
| now()             | sleep(3) | now()             |
+---------------------+----------+---------------------+
| 2011-03-01 10:51:43 |       0 | 2011-03-01 10:51:43 |
+---------------------+----------+---------------------+
1 row in set (3.02 sec)

mysql> select sysdate(),sleep(3),sysdate();
+---------------------+----------+---------------------+
| sysdate()          | sleep(3) | sysdate()          |
+---------------------+----------+---------------------+
| 2011-03-01 10:52:09 |       0 | 2011-03-01 10:52:12 |
+---------------------+----------+---------------------+
1 row in set (3.00 sec)
可以看到，雖然中途 sleep 3 秒，但 now() 函式兩次的時間值是相同的； sysdate() 函式兩次得到的時間值相差 3 秒

也可以只取當前日期或者當前時間
Curdate(): 獲得當前日期

mysql> select curdate();
+------------+
| curdate()  |
+------------+
| 2011-03-01 |
+------------+
1 row in set (0.01 sec)

Curtime():獲得當前時間（time）函式

mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| 10:55:12  |
+-----------+
1 row in set (0.00 sec)

二、 Mysql日期時間的抽取extract

透過這一功能，我們可以從一個時間中抽取自己想要的部分，例如
mysql> set @ct='2011-03-01 11:16:14.123456';
Query OK, 0 rows affected (0.01 sec)
設定變數ct為某一時間值，精確到微妙

獲取其日期值
mysql> select date(@ct);
+------------+
| date(@ct)  |
+------------+
| 2011-03-01 |
+------------+
1 row in set (0.00 sec)

檢視此日期所屬季度
mysql> select quarter(@ct);
+--------------+
| quarter(@ct) |
+--------------+
|          1 |
+--------------+
1 row in set (0.00 sec)

檢視此日期屬於當年哪一週
mysql> select week(@ct);
+-----------+
| week(@ct) |
+-----------+
|       9 |
+-----------+
1 row in set (0.00 sec)
另外還有year(),day(),hour(),minute(),second()等，在此不一一贅述。

採用extract()，也可以實現類似的功能，語法格式為extract(year from @ct)，
不足之處在於需要多敲幾次鍵盤

Dayof函式:
Dayofweek(),dayofmonth(),dayofyear()分別返回日期再一週、一月以及一年中的位置
mysql> select dayofweek(@ct);
+----------------+
| dayofweek(@ct) |
+----------------+
|             3 |
+----------------+
1 row in set (0.00 sec)
注意：其實3月1號是星期二，但是返回數字3，因為是從Sunday開始算起的(1=Sunday,2=Monday,…)

mysql> select dayofmonth(@ct);
+-----------------+
| dayofmonth(@ct) |
+-----------------+
|             1 |
+-----------------+
1 row in set (0.00 sec)

mysql> select dayofyear(@ct);
+----------------+
| dayofyear(@ct) |
+----------------+
|          60 |
+----------------+
1 row in set (0.00 sec)

Week()函式
檢視日期屬於當年的第幾周
mysql> select weekofyear(@ct);
+-----------------+
| weekofyear(@ct) |
+-----------------+
|             9 |
+-----------------+
1 row in set (0.00 sec)

返回星期名和月份名的函式
Dayname()—計算日期是星期幾
mysql> select dayname(@ct);
+--------------+
| dayname(@ct) |
+--------------+
| Tuesday    |
+--------------+
1 row in set (0.02 sec)

Monthname()—計算日期是哪一月
mysql> select monthname(@ct);
+----------------+
| monthname(@ct) |
+----------------+
| March       |
+----------------+
1 row in set (0.00 sec)

Last_day(): 返回月份中最後一天
mysql> select now();
+---------------------+
| now()             |
+---------------------+
| 2011-03-01 13:15:00 |
+---------------------+
1 row in set (0.00 sec)

mysql> select last_day(now());
+-----------------+
| last_day(now()) |
+-----------------+
| 2011-03-31    |
+-----------------+
1 row in set (0.00 sec)
透過該函式，可以計算出當前月份有多少天
mysql> select now(),day(last_day(now())) ;
+---------------------+----------------------+
| now()             | day(last_day(now())) |
+---------------------+----------------------+
| 2011-03-01 13:17:12 |                31 |
+---------------------+----------------------+
1 row in set (0.00 sec)

三、Mysql的日期時間計算函式
Date_add(): 為日期增加一個時間間隔
具體語法為date_add(@ct, interval num year/quarter/month/week/day/hour/minute/secont/microsecond);
注意:此函式並不改變變數@ct的實際值
mysql> set @ct=now();
Query OK, 0 rows affected (0.00 sec)

mysql> select @ct;
+---------------------+
| @ct                |
+---------------------+
| 2011-03-01 15:09:16 |
+---------------------+
1 row in set (0.00 sec)

mysql> select date_add(@ct,interval 1 day);
+------------------------------+
| date_add(@ct,interval 1 day) |
+------------------------------+
| 2011-03-02 15:09:16       |
+------------------------------+
1 row in set (0.00 sec)

mysql> select @ct;
+---------------------+
| @ct                |
+---------------------+
| 2011-03-01 15:09:16 |
+---------------------+
1 row in set (0.00 sec)

mysql> select date_add(@ct,interval 1 week);
+-------------------------------+
| date_add(@ct,interval 1 week) |
+-------------------------------+
| 2011-03-08 15:09:16          |
+-------------------------------+
1 row in set (0.00 sec)

類似功能還有adddate(),addtime()等函式，與之相對應的是date_sub()，顧名思義就是日期減法

另類日期函式
Period_add(P,N): 日期加/減去N月，其中P的格式應為yyyymm或yymm
Period_diff(P1,P2): 日期p1-p2，返回N個月

mysql> select period_add(201103,2),period_add(201103,-2) ;
+----------------------+-----------------------+
| period_add(201103,2) | period_add(201103,-2) |
+----------------------+-----------------------+
|             201105 |             201101 |
+----------------------+-----------------------+
1 row in set (0.00 sec)

mysql> select period_diff('201103','201101');
+--------------------------------+
| period_diff('201103','201101') |
+--------------------------------+
|                            2 |
+--------------------------------+
1 row in set (0.00 sec)

日期時間相減函式
Datediff(date1,date2): 兩個日期date1-date2
mysql> select datediff('2011-03-09','2011-03-01');
+-------------------------------------+
| datediff('2011-03-09','2011-03-01') |
+-------------------------------------+
|                                  8 |
+-------------------------------------+
1 row in set (0.00 sec)

mysql> select datediff('2011-03-01','2011-03-09');
+-------------------------------------+
| datediff('2011-03-01','2011-03-09') |
+-------------------------------------+
|                               -8 |
+-------------------------------------+
1 row in set (0.00 sec)

Timediff(time1,time2):兩個時間相減
mysql> select timediff('2011-03-03 15:33:00','2011-03-02 15:33:59');
+-------------------------------------------------------+
| timediff('2011-03-03 15:33:00','2011-03-02 15:33:59') |
+-------------------------------------------------------+
| 23:59:01                                           |
+-------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff('15:33:00','15:33:59');
+---------------------------------+
| timediff('15:33:00','15:33:59') |
+---------------------------------+
| -00:00:59                      |
+---------------------------------+
1 row in set (0.00 sec)

四  mysql日期、時間轉換函式

Time_to_sec(time): 時間—>秒轉換函式
Sec_to_time(num): 秒--&gt時間轉換函式

mysql> select time_to_sec('01:00:00');
+-------------------------+
| time_to_sec('01:00:00') |
+-------------------------+
|                   3600 |
+-------------------------+
1 row in set (0.00 sec)

mysql> select sec_to_time(3600);
+-------------------+
| sec_to_time(3600) |
+-------------------+
| 01:00:00       |
+-------------------+
1 row in set (0.00 sec)

To_days(date): 日期--&gt天轉換函式起始日期為0000-00-00
From_days(num): 天--&gt日期將數字轉換為具體的日期
mysql> select to_days('2011-03-01');
+-----------------------+
| to_days('2011-03-01') |
+-----------------------+
|             734562 |
+-----------------------+
1 row in set (0.00 sec)

mysql> select from_days(734562);
+-------------------+
| from_days(734562) |
+-------------------+
| 2011-03-01       |
+-------------------+
1 row in set (0.00 sec)

Str_to_date(str,date): 字串--&gt日期轉換函式
可以將一些雜亂無章的字元轉換為日期格式
mysql> select str_to_date('01.03.2011', '%m.%d.%Y');
+---------------------------------------+
| str_to_date('01.03.2011', '%m.%d.%Y') |
+---------------------------------------+
| 2011-01-03                         |
+---------------------------------------+
1 row in set (0.00 sec)

mysql> select str_to_date('01/03/2011', '%m/%d/%Y');
+---------------------------------------+
| str_to_date('01/03/2011', '%m/%d/%Y') |
+---------------------------------------+
| 2011-01-03                         |
+---------------------------------------+
1 row in set (0.00 sec)

小練習：
以表justin為例，目前該表總共有270多萬條資料
mysql> select count(*) from justin;
+----------+
| count(*) |
+----------+
|  2725403 |
+----------+
1 row in set (0.00 sec)

現在對其做一些統計

查詢過去30天總共有多少資料
mysql> select count(*) from justin where to_days(curdate())- to_days(create_time)<=30;
+----------+
| count(*) |
+----------+
|  2367518 |
+----------+
1 row in set (3.38 sec)

mysql> select count(*) from justin where datediff(curdate(),create_time) <=30;
+----------+
| count(*) |
+----------+
|  2367518 |
+----------+
1 row in set (3.29 sec)

檢視每月第一天的資料
mysql> select count(*) from justin where dayofmonth(create_time)=1;
+----------+
| count(*) |
+----------+
| 161293 |
+----------+
1 row in set (3.14 sec)

檢視11年1月31日之前的資料
mysql> select count(*) from justin where create_time <='2011-01-31 00:00:00';
+----------+
| count(*) |
+----------+
| 413797 |
+----------+
1 row in set (0.17 sec)

檢視11年整個二月份的資料
mysql> select count(*) from justin where monthname(create_time)='February' and year(create_time)=2011;
+----------+
| count(*) |
+----------+
|  2149284 |
+----------+
1 row in set (3.94 sec)

檢視11年每個週日的累積資料
mysql> select count(*) from justin where dayname(create_time)='Sunday' and year(create_time)=2011;
+----------+
| count(*) |
+----------+
| 479033 |
+----------+
1 row in set (3.88 sec)

檢視每天零點時分插入的資料總和
mysql> select count(*) from justin where time(create_time)='00:00:00';
+----------+
| count(*) |
+----------+
|    37 |
+----------+
1 row in set (3.99 sec)

mysql日期函式小結及個人實驗

相關文章