Working with Dates and Times - Database Design Manual: Using MySQL for Windows - page 125

The timeperiod will be a value, followed by the type of time period from Table 11.4.For
example, to find out what the date was this time last week, we can use:

DATE_SUB('2002-12-23', INTERVAL 7 DAY )

And we can take time away from a date as follows:

DATE_SUB('2002-12-23', INTERVAL 1 SECOND )

Figure 11.12 shows these two functions running, using the following script:

SELECT '2002-12-23' AS TodaysDate,

DATE_SUB('2002-12-23', INTERVAL 7 DAY ) AS lastweek,
DATE_SUB('2002-12-23', INTERVAL 1 SECOND ) AS yesterday

SUBDATE
The SUBDATE() function works exactly the same as the DATE_SUB() function just
described. The format is therefore:

SUBDATE( aDate, INTERVAL timeperiod )

Please refer to the DATE_SUB section above for further information.

TO_DAYS
The TO_DAYS() function converts a date into the number of days since year 0. You pass the
function a date as follows:

TO_DAYS(aDate)

So to convert today's date into days we can use:

TO_DAYS('2002-12-23') as ToDays

Figure 11.12 DATE_SUB() subtracts time periods from given dates.