Detailed explanation of the method of comparing dates in MySQL

If there is a table product with a field add_time, whose data type is datetime, someone might write the SQL like this:

The code is as follows

select * from product where add_time = '2013-01-12'

For this statement, if the format you store is YY-mm-dd, then it's OK. If the format you store is: 2013-01-12 23:23:56, then you are in trouble. This is the part where you can use the DATE() function to return the date, so this SQL should be processed as follows:

The code is as follows

select * from product where Date(add_time) = '2013-01-12'

Another one, what if you want to query the products added in January 2013?

The code is as follows

select * from product where date(add_time) between '2013-01-01' and '2013-01-31'

You can also write:

select * from product where Year(add_time) = 2013 and Month(add_time) = 1

Now you should know the role of MySQL date functions in dealing with date comparison problems, right?

Its date_col value is within the last 30 days:

The code is as follows

mysql> SELECT something FROM table 
 WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;
DAYOFWEEK(date)

Returns the day of the week index of date (1=Sunday, 2=Monday, ... 7=Saturday). These index values ​​correspond to the ODBC standard.

The code is as follows

mysql> select DAYOFWEEK('1998-02-03'); 
 -> 3 
WEEKDAY(date)

Returns the day of the week index of date (0=Monday, 1=Tuesday, ... 6=Sunday).

The code is as follows

mysql> select WEEKDAY('1997-10-04 22:23:00'); 
 -> 5 
 mysql> select WEEKDAY('1997-11-05'); 
 -> 2 
DAYOFMONTH(date)

Returns the day of the month in date, in the range 1 to 31.

The code is as follows

mysql> select DAYOFMONTH('1998-02-03'); 
 -> 3 
DAYOFYEAR(date)

Returns the day of the year for date, in the range 1 to 366.

The code is as follows

mysql> select DAYOFYEAR('1998-02-03'); 
 -> 34 
MONTH(date)

Returns the month of date, ranging from 1 to 12.

The code is as follows

mysql> select MONTH('1998-02-03'); 
 -> 2 
DAYNAME(date)

Returns the day of the week of date.

The code is as follows

mysql> select DAYNAME("1998-02-05"); 
 -> 'Thursday' 
MONTHNAME(date)

Returns the name of the month in date.

The code is as follows

mysql> select MONTHNAME("1998-02-05"); 
 -> 'February' 
QUARTER(date)

Returns the quarter of the year for date, in the range 1 to 4.

The code is as follows

mysql> select QUARTER('98-04-01'); 
 -> 2

If you want to have a more in-depth and systematic study of MySQL, you can refer to the classic book "MySQL King's Road to Promotion".

Summarize

The above is the method of comparing dates in MySQL that I introduced to you. I hope it will be helpful to you. If you have any questions, please leave me a message and I will reply to you in time. I would also like to thank everyone for their support of the 123WORDPRESS.COM website!