MySQL's judgment on time function

function to get the current time: Now (), Curdate (), Curtime ()

Now (): 2008-12-29 16:25:46

Curdate (): 2008-12-29

Curtime (): 16:25:46

Gets the data in the table that is greater than or equal to today, and less than tomorrow:

SELECT * FROM table WHERE createdtime >= curdate () and Createdtime < Date_sub (Curdate (), INTERVAL-1 Day)

Today is August 01, 2016.

Date_sub (' 2016-08-01 ', Interval 1 day) says 2016-07-31
Date_sub (' 2016-08-01 ', Interval 0 day) says 2016-08-01
Date_sub (' 2016-08-01 ', interval-1 day) says 2016-08-02

Date_sub (Curdate (), Interval 1 day) represents 2016-07-31
Date_sub (Curdate (), Interval-1 Day) 2016-08-02
Date_sub (Curdate (), Interval 1 month) represents 2016-07-01
Date_sub (Curdate (), Interval-1 month) represents 2016-09-01
Date_sub (Curdate (), Interval 1 year) represents 2015-08-01
Date_sub (Curdate (), Interval-1 year) represents 2017-08-01

MySQL's judgment on time function