1. Obtain day data: TO_DAYS (a.last_operation_date) = TO_DAYS (NOW ())
a.last_operation_date: time saved in the database field, now () indicates the current time
TO_DAYS (now ()): returns from year 0 to start now () a number of days now
2.curdate (): Get the current date
curtime (): Get the current time every minute
now (): Gets the current date and time
Note: The judge stepped on today's date pit: time between curdate () and curdate () + 1: // [2018.08.08 00:00:00 2018.08.09 00:00:00] both contain
3.date_sub (date, INTERVAL expr type) function
data: Time
expr: Positive Negative interval backwards when the number of days or years ahead spaced intervals
type: When possible date
