A. timestampdiff() 传三个参数，第一个时间类型如年，月，日，第二个开始时间，第三个结束时间
select test_name, timestampdiff(YEAR,create_time,end_time) y_date from test_table;--计算时间

+-----------+--------+
| test_name | y_date |
+-----------+--------+
| 哈罗德| 29 |
| 哈罗德| 17 |
| 格温| 13 |
| 班尼|110 |
+-----------+--------+

B. INTERVAL ndayday还可以替换为年月等
select now()+ INTERVAL 1 day; --表示明天

+-----------------------+
| now()+ INTERVAL 1 day |
+-----------------------+
| 2018-12-07 09:52:03 |
+-----------------------+

C. last_day() 括号内加个时间日期，表示月末
select last_day(now());--表示月末

+-----------------+
| last_day(now()) |
+-----------------+
| 2018-12-31|
+-----------------+

D. extract(day from now())表示某月第几天，day 还可以替换为year,month 等
select date_sub(date(now()),interval extract(day from now()) - 1 day) as 'month_firstday'; 月初

+----------------+
| month_firstday |
+----------------+
| 2018-12-01 |
+----------------+

E. date_format()把一个日期/时间转换成各种各样的字符串格式

select date_format(now(),'%Y-%m-%d %h:%i:%s');%Y：年，% m:月， %M：英文月，%d: 日， %D ：英文日， %h:小时，%H:24小时制，%i:分钟，%s:秒

+----------------------------------------+
| date_format(now(),'%Y-%m-%d %h:%i:%s') |
+----------------------------------------+
| 2018-12-06 10:28:04|
+----------------------------------------+

F. str_to_date()把一个字符串格式日期/时间转换成时间
select str_to_date('07.10.2017 08:09:30', '%m.%d.%Y %h:%i:%s') as st_to_d;

+---------------------+
| st_to_d |
+---------------------+
| 2017-07-10 08:09:30 |
+---------------------+
1 row in set (0.06 sec)

G. date_add(),date_sub()
select date_add(now(), interval 1 day) as add_day; 加一天， 表示明天

+---------------------+
| add_day |
+---------------------+
| 2018-12-07 10:46:50 |
+---------------------+
1 row in set (0.00 sec)

select date_add(now(), interval 1 day) as add_day; 减一天，表示昨天

+---------------------+
| sub_day |
+---------------------+
| 2018-12-05 10:48:48 |
+---------------------+
1 row in set (0.00 sec)

H. select week(now());年中第几周
select quarter(now()); 季度
select dayofweek(now()); 一周中第几天
select dayofmonth(now());一个月第几天
select dayofyear(now()); 一年第几天
show variables like 'lc_time_names';
select dayname(now()),monthname(now());英文周几，英文月份

+----------------+------------------+
| dayname(now()) | monthname(now()) |
+----------------+------------------+
| Thursday | December |
+----------------+------------------+

set lc_time_names='zh_CN'; 时间名称改为中文

+----------------+------------------+
| dayname(now()) | monthname(now()) |
+----------------+------------------+
| 星期四 | 十二月 |
+----------------+------------------+