Syntax:
SUBDATE(date,INTERVAL expr type), SUBDATE(expr,days)

When invoked with the INTERVAL form of the second argument, SUBDATE()
is a synonym for DATE_SUB(). For information on the INTERVAL argument,
see the discussion for DATE_ADD().

mysql> SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY);
        -> '1997-12-02'
mysql> SELECT SUBDATE('1998-01-02', INTERVAL 31 DAY);
        -> '1997-12-02'

The second form allows the use of an integer value for days. In such
cases, it is interpreted as the number of days to be subtracted from
the date or datetime expression expr.

mysql> SELECT SUBDATE('1998-01-02 12:00:00', 31);
        -> '1997-12-02 12:00:00'

Note: You cannot use format "%X%V" to convert a year-week string to a
date because the combination of a year and week does not uniquely
identify a year and month if the week crosses a month boundary. To
convert a year-week to a date, then you should also specify the
weekday:

mysql> SELECT STR_TO_DATE('200442 Monday', '%X%V %W');
        -> '2004-10-18'
