MySQL's time difference function (TIMESTAMPDIFF, DATEDIFF), date conversion calculation function (date_add, day, date_format, str_to_date)
- Time difference function (TIMESTAMPDIFF, DATEDIFF)
You need to use MySQL to calculate the time difference, use TIMESTAMPDIFF, DATEDIFF, and record the experimental results.
--0
select datediff(now(), now());
--2
select datediff('2023-09-22 23:59:00', '2023-09-20 00:00:00');
--2
select datediff('2023-09-22 00:00:00', '2023-09-20 23:59:00');
--1
select TIMESTAMPDIFF(DAY, '2023-09-20 23:59:00', '2023-09-22 00:00:00');
--2
select TIMESTAMPDIFF(DAY, '2023-09-20 00:00:00', '2023-09-22 00:00:00');
--2
select TIMESTAMPDIFF(DAY, '2023-09-20 00:00:00', '2023-09-22 12:00:00');
--2
select TIMESTAMPDIFF(DAY, '2023-09-20 00:00:00', '2023-09-22 23:59:00');
--71
select TIMESTAMPDIFF(HOUR, '2023-09-20 00:00:00', '2023-09-22 23:00:00');
--4260
select TIMESTAMPDIFF(MINUTE, '2023-09-20 00:00:00', '2023-09-22 23:00:00');
- Date conversion calculation function (date_add, day, date_format, str_to_date)
DATE_ADD() function usage
Definition and Usage: The DATE_ADD() function adds a specified time interval to a date.
DATE_ADD(date,INTERVAL expr type)
The date parameter is a legal date expression. The expr parameter is the time interval you wish to add.
The type parameter can be the following values: DAY, WEEK, etc.
DATE_ADD("2023-09-20 ",INTERVAL 2 day)
结果："2023-09-22 "
DATE_ADD("2023-09-20 ",INTERVAL -2 day)
结果："2023-09-18 "
date_format(): Returns the formatted time and date
grammar:
DATE_FORMAT(date,format);
parameter:
date: the valid time and date that needs to be formatted
format: A string in a predefined format, with a percent sign (%) in front of each specifier.
SELECT id,
name,
DATE_FORMAT(start_time, '%Y-%m-%d %H:%i:%S') start_time,
DATE_FORMAT(end_time, '%Y-%m-%d %H:%i:%S') end_time
FROM user
The STR_TO_DATE function is used to convert a string into a date/time value
The functions of the STR_TO_DATE function and the DATE_FORMAT function are opposite.
Syntax format
STR_TO_DATE(str,format)
srt: string to be formatted as date (input string)
format: the format string to use
If str cannot be parsed according to format, the STR_TO_DATE function will return NULL
If any of the parameters is NULL, the STR_TO_DATE function returns NULL
Predefined description character list:
commonly used format formats
Practice example
Convert string to DATE value
-- 2023-09-20
SELECT STR_TO_DATE('20,9,2023','%d,%m,%Y');
-- 2023-09-20
SELECT STR_TO_DATE('2023-09-20 11:30:00','%Y-%m-%d');
-- 2023-08-01
SELECT STR_TO_DATE('August,1,2023', '%M,%e,%Y');
-- 2023-08-10
SELECT STR_TO_DATE('August 10 2023', '%M %d %Y');
-- 2023-08-15
SELECT STR_TO_DATE('Monday, August 15, 2023', '%W,%M %e, %Y');
将字符串转换为DATETIME值
-- 2023-09-20 11:30:00
SELECT STR_TO_DATE('20230920 1130','%Y%m%d %h%i');
-- 2023-09-20 11:30:00
SELECT STR_TO_DATE('2023-09-20 11:30:00','%Y-%m-%d %H:%i:%s');
-- 2023-09-20 10:40:10
SELECT STR_TO_DATE('2023,9,20 10,40,10', '%Y,%m,%d %h,%i,%s');
STR_TO_DATE函数在根据格式字符串format解析输入字符串str时，忽略输入字符串str末尾的额外字符
-- 2023-09-20
SELECT STR_TO_DATE('20,9,2023 extra characters','%d,%m,%Y');
-- 2023-09-20 11:30:00
SELECT STR_TO_DATE('20230920 1130 extra characters','%Y%m%d %h%i');
如果输入字符串str是非法的，则STR_TO_DATE函数返回NULL
-- NULL
SELECT STR_TO_DATE('2023','%Y');
-- NULL
SELECT STR_TO_DATE('11','%h');
-- NULL
SELECT STR_TO_DATE('1130','%h%i');
-- NULL
SELECT STR_TO_DATE('113005','%h%i%s');
-- NULL
SELECT STR_TO_DATE('August,20,2023', '%M %e %Y');
-- NULL
SELECT STR_TO_DATE('Monday, August 20, 2023', '%W %M %e %Y');
-- 用日期与字符串转换，计算当月第一天、下月第一天
select curdate() as '当前日期',
DATE_FORMAT(curdate(), '%Y-%m') as '当前月份',
str_to_date(concat(DATE_FORMAT(curdate(), '%Y-%m'), '-01'), '%Y-%m-%d') as '当前月的第一天',
date_add(str_to_date(concat(DATE_FORMAT(curdate(), '%Y-%m'), '-01'), '%Y-%m-%d'), interval 1 month) as '下月的第一天';
-- 当前月的最后一天
select last_day(curdate());
-- 下月第一天
select date_add(last_day(curdate()), interval 1 day);
-- 当天为当月的第几天
select day(curdate());
-- 当月第一天
select date_add(curdate(), interval 1-(day(curdate())) day);