如何在mysql中获取日期的一周的第一天?

Suppose I have 2011-01-03 and I want to get the first of the week, which is sunday, which is 2011-01-02, how do I go about doing that?

原因是我有这个查询:

select 
  YEAR(date_entered) as year, 
  date(date_entered) as week,   <-------This is what I want to change to select the first day of the week.
  SUM(1) as total_ncrs, 
  SUM(case when orgin = picked_up_at then 1 else 0 end) as ncrs_caught_at_station 
from sugarcrm2.ncr_ncr 
where 
sugarcrm2.ncr_ncr.date_entered > date('2011-01-01') 
and orgin in( 
'Silkscreen', 
'Brake', 
'Assembly', 
'Welding', 
'Machining', 
'2000W Laser', 
'Paint Booth 1', 
'Paint Prep', 
'Packaging', 
'PEM', 
'Deburr', 
'Laser ', 
'Paint Booth 2', 
'Toolpath' 
) 
and date_entered is not null 
and orgin is not null 
AND(grading = 'Minor' or grading = 'Major') 
 and week(date_entered) > week(current_timestamp) -20 
group by year, week(date_entered) 
order by year   asc, week asc 

是的，我意识到 origin 拼写错误，但它在我之前就在这里，所以我无法更正它，因为有太多内部应用程序引用它.

DELIMITER ;;
CREATE FUNCTION FIRST_DAY_OF_WEEK(day DATE)
RETURNS DATE DETERMINISTIC
BEGIN
  RETURN SUBDATE(day, WEEKDAY(day));
END;;
DELIMITER ;

SELECT FIRST_DAY_OF_WEEK('2011-01-03');