MySQL: Add 30 days to a value in the table

I'm trying to use the ADDDATE function on a value in the table.

UPD开发者_Python百科ATE credit SET addOns=ADDDATE(addOns, INTERVAL 30)

addOns is where I store the datetime. Why can I not add 30 days?

I also tried

UPDATE credit SET addOns=ADDDATE(SELECT addOns FROM credit, INTERVAL 30)

UPDATE credit SET addOns=ADDDATE(addOns, INTERVAL 30 DAY)
-- Or
UPDATE credit SET addOns=ADDDATE(addOns, 30)

If you specify INTERVAL, you must specify the unit; if you don't specify INTERVAL it will default to days.

UPDATE credit SET addOns=ADDDATE(addOns, INTERVAL 30 DAY)

Without interval keyword.

UPDATE credit SET addOns=ADDDATE(addOns, 30)

date_add(yourDate, INTERVAL 30 DAY)