Update date to 1st day of the month in MySQL?

Question

How would I go about updating the dates in a MySQL table to the first day of the month?

For example, the data looks like this:

1   2013-01-13
2   2013-02-11
3   2013-02-01
4   2013-01-30
5   2013-03-27

...and I would like it to look like this...

1   2013-01-01
2   2013-02-01
3   2013-02-01
4   2013-01-01
5   2013-03-01

Answer 1

You can convert it to string to get the year and month and concatenate it with 01 .

UPDATE  tableName
SET     dateField = CONCAT(DATE_FORMAT(dateField, '%Y-%m-'), '01')

• SQLFiddle Demo

Answer 2

UPDATE tableName SET date = DATE_SUB(date,INTERVAL DAYOFMONTH(date)-1 DAY)

日期和时间函数