php - MySQL get data older than 30 minutes and perform some tasks -

i trying make coupon system, got stuck something. want make function gets data coupon_session time (datetime) older 30 minutes. each of results, want fetch "code" row, , after want delete row.

i've figured out how retrieve data, rest kinda hard me. guys bit?

this code fetching > 30 min old rows:

mysql_query("get * `coupon_session` timestampdiff(minute,time,now()) > 30"); 

the code fetch want is:

select cs.code coupon_session cs time < date_sub(now(), interval 30 minute); 

deleting problem, because value of now() changes. have several choices, such as:

• get list of ids delete in application , delete (probably safest method).
• calculate "now" in application , use same value select , delete (also safe).
• calculate maximum time returned select , use subsequent delete.