MySQL winter vacation self-study 2022 12 (5)

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--  Date function 
-- 1, Get the timestamp （ Millisecond value ）
select unix_timestamp();

-- 2, Convert a date string to a millisecond value 
select unix_timestamp('2021-12-21 08:08:08');

-- 3, Converts the timestamp millisecond value to a date in the specified format 
select from_unixtime(1640045288,'%Y-%m-%d %H:%i:%s');# Capitalization y And lowercase y Different , Check the table if necessary 
-- 4, Get the current date 
select curdate();
select current_date;

-- 5, Get the current hour, minute, second 
select current_time();
select curtime();

-- 6, Get date   and   Minutes and seconds 
select current_timestamp();

-- 7, Get the date from the date string 
select date('2022-12-12 12:34:56');

-- 8, Get interpolation between dates 
select datediff('2021-12-23','2008-08-08');#4885, The front minus the back 
select datediff('2008-08-08','2021-12-23');#4885
select datediff(current_time(),'2008-08-08');

-- 9 Get the difference in time （ Minutes and seconds ）
select timediff('12:12:34','10:18:56');

-- 10, Date formatting 
select date_format('2021-1-1 1:1:1','%Y-%m-%d %H:%i:%s');

-- 11, Convert string to date 
select str_to_date('2021-1-1 1:1:1','%Y-%m-%d %H:%i:%s');

-- 12, Subtract the date 
select date_sub('2021-10-01',interval 2 day);
select date_sub('2021-10-01',interval 2 month);

-- 13, Add the date 
select date_add('2021-10-01',interval 2 day);

-- 14, Get the hour from the date (year,month, Fine )
select extract(hour from '2021-1-2 3:4:4');

-- 15, Get the last day of the month in which the given date is located 
select last_day('2021-8-13');#2021-08-31

-- 16, Gets the date of the year and the specified number of days eg,2021 The fifty third day of the year 
select makedate('2021',53);

-- 17, Get the year, minute and second according to the date 
select year('2021-1-2 3:4:4');
select month('2021-1-2 3:4:4');
select minute('2021-1-2 3:4:4');
select quarter('2021-1-2 3:4:4');# Get Quarterly 

-- 18, Get information based on date 
select monthname('2021-1-2 3:4:4');
select dayname('2021-1-2 3:4:4');# What day , english 
select dayofmonth('2021-1-2 3:4:4');# What day of the month 
select dayofweek('2021-1-2 3:4:4');# What day of the week  1 It's Sunday 
select dayofyear('2021-1-2 3:4:4');# What day of the year 
select week('2021-1-2 3:4:4');# Week , The scope is 0-53
select weekday('2021-1-2 3:4:4');#0 It means Monday 
select weekofyear('2021-1-2 3:4:4');
select yearweek('2021-3-01');
--  Get the current date and time 
select now();