MySQL date and time function, varchar and date are mutually converted

1.mysql Get system time

1. Get current system time

Add one after that 0, You can convert the current queried time into digital output .

1. Get current date + Time

function ：

function	explain
now()	The function gets the value at the beginning of execution
sysdate()	Get values dynamically during function execution

select now(), sysdate();

2. Get current date

function
curdate()
current_date()
current_date

select curdate(), current_date(), current_date, CURRENT_DATE() + 0;

3. Get the current time

function
curtime()
current_time()
current_time

select curtime(), current_time(), current_time, current_time()+0;

4. obtain UTC Time

select utc_date()+0, utc_time(), utc_timestamp;

2. Get yesterday 、 today 、 Tomorrow's , Last hour , The next hour

1. yesterday 、 today 、 Tomorrow,

Date subtraction

function	explain
DATE_SUB(date,INTERVAL expr type)	date： Legal date expression expr： The time interval type：second、hour、day、minute…

date + Time ：

select date_sub(now(),interval 1 day) as ' yesterday ',
	   date_sub(now(),interval 0 day) as ' today ',
	   date_sub(now(),interval -1 day) as ' Tomorrow, '

date ：

select date_sub(curdate(),interval 1 day) as ' yesterday ',
	   date_sub(curdate(),interval 0 day) as ' today ',
	   date_sub(curdate(),interval -1 day) as ' Tomorrow, '

2. Last hour , front 30 minute , 45 minutes later

select date_sub(now(),interval 1 hour) as ' Last hour ',
	   date_sub(now(),interval 30 minute) as ' front 30 minute ',
	   date_sub(now(),interval 45 minute) as ' 45 minutes later ';

3. Date subtraction 、 Time minus

function	explain
DATEDIFF(date1,date2)	date1： Legal date expression date2： Legal date expression
TIMEDIFF(time1,time2)	time1： Legal time expression time2： Legal time expression

select datediff(now(),date_sub(now(),interval 1 day)) as ' Date subtraction ';

select timediff(now(),date_sub(date_sub(now(),interval 45 minute),interval 1 day)) as ' Time minus ';

4. Date addition 、 Time adds up

Date addition

function	explain
DATE_ADD(date,INTERVAL expr type)	see DATE_SUB
TIMEDIFF(time1,time2)	time1： Legal time expression time2： Legal time expression

select date_add(now(),interval 3 day) as ' Three days later ', 
	   date_add(now(),interval 30 minute) as ' After half an hour '; 

5. Add ——sleep()

function	explain
sleep()	Give Way SQL The statement executes for a period of time , The unit is seconds

select sleep(5), now(), sysdate();

2.mysql Of varchar And date Transformation

1.varchar turn date

function	Format	explain
str_to_date	STR_TO_DATE(str,fmt)	str： character string fmt： Time format

select str_to_date('2022 7 26','%Y %m %d') as ' today ',
	   str_to_date('2022,27,7','%Y,%d,%m') as ' Tomorrow, ',
	   str_to_date('2022725','%Y%m%d') as ' yesterday ';

select str_to_date('26-7-2022-123456', '%d-%m-%Y') as ' today ',
	   str_to_date('2022', '%Y') as ' This year, ';

select str_to_date('221322','%H%i%s') as ' Now? 1',
	   str_to_date('22:13:22','%H:%i:%s') as ' Now? 2';

select str_to_date('221322','%H%i%s') as ' Now? 1',
	   str_to_date('22:13:22','%H:%i:%s') as ' Now? 2',
	   str_to_date('2022,7,26 22:13:22','%Y,%m,%e %H:%i:%s') as ' Now? 3';

2.date turn varchar

function	Format	explain
date_format	DATE_FORMAT(date,format)	date： The legal date format ： Specified date / Time output format

select date_format(now(), '%Y %m %d') as ' today ',
	   date_format(now(), '%Y-%m-%d %H:%i:%s') as ' Now? '; 

3. Add

Get the string of a certain day and a certain time

select date_format(trim(concat((select DATE_SUB(curdate(),INTERVAL 0 DAY)),' 00:00:00')), '%Y-%m-%d %H:%i:%s') as ' Early this morning ',
	   date_format(trim(concat((select DATE_SUB(curdate(),INTERVAL 1 DAY)),' 00:00:00')), '%Y-%m-%d %H:%i:%s') as ' In the morning yesterday ',
	   date_format(trim(concat((select DATE_SUB(curdate(),INTERVAL -1 DAY)),' 00:00:00')), '%Y-%m-%d %H:%i:%s') as ' Tomorrow morning ';