第一部分日期和时间函数
3.3 MySQLOF 函数：
1.NOW():当前日期+时间;
设T=NOW();
----该天分别在周/月/年中的位置----
1.DAYOFWEEK(T);（1= Sunday,2= Monday, ...,7= Saturday）
2.DAYOFMONTH(T);
3.DAYOFYEAR(T);
4.----------------
5.WEEK(T);
6.WEEKOFYEAR(T);等同于WEEK(T);
7.WEEKDAY(T); (0= Monday,1= Tuesday, ...,6= Sunday)；
MariaDB[study_db]>SELECTNOW(),CURDATE(),CURTIME();
MariaDB[study_db]>SELECTDAYOFWEEK(NOW()), DAYOFMONTH(NOW()), DAYOFYEAR(NOW());
+------------------+-------------------+------------------+
| DAYOFWEEK(NOW()) | DAYOFMONTH(NOW()) | DAYOFYEAR(NOW()) |
+------------------+-------------------+------------------+
|2|19|354|
+------------------+-------------------+------------------+
1rowinset(0.00sec)
MariaDB[study_db]>SELECTWEEK(NOW()), WEEKOFYEAR(NOW()),WEEKDAY(NOW()), YEARWEEK(NOW());
+-------------+-------------------+----------------+-----------------+
| WEEK(NOW()) | WEEKOFYEAR(NOW()) |WEEKDAY(NOW()) | YEARWEEK(NOW()) |
+-------------+-------------------+----------------+-----------------+
|51|51|0|201651|
+-------------+-------------------+----------------+-----------------+
1rowinset(0.00sec)
3.4计算函数
------加--------
1. DATE_ADD(T, interval1YEAR);
2. DATE_ADD(T, interval1SQUARTER);
4. --------减------
5. DATE_SUB(T, interval1YEAR);
6.
6.加减的参数:MONTH/DAY/HOUT/SECOND/MINUTE
实例代码
MariaDB [study_db]> SELECT publication_date, DATE_ADD(publication_date, interval1year) FROM new_books;
+------------------+---------------------------------------------+
| publication_date | DATE_ADD(publication_date, interval1year) |
+------------------+---------------------------------------------+
|2016-12-03|2017-12-03|
|2016-12-02|2017-12-02|
3.5MySQL日期、时间相减函数
1.DATEDIFF(date1,date2)：两个日期相减date1 date2，返回天数。
2.TIMEDIFF(time1,time2):两个日期相减time1 time2，返回time差值。
实例
MariaDB [study_db]> SELECT DATEDIFF(DATE(NOW()), '2016-12-31') AS '天数差',
-> TIMEDIFF(TIME(NOW()), '24:24:00') AS '时间差';
+--------+-----------+
|天数差|时间差|
+--------+-----------+
| -12 | -09:08:10 |
+--------+-----------+
1 row in set (0.00 sec)
