MySQL prevent user to take codes from other user

Question

Hello have the following query:

SELECT code FROM tbl_codes WHERE used='0' ORDER BY RAND() LIMIT 2;

This will result in 2 codes with unique value (ex: code = 1 code = 2). After that I will update the table that those codes are used with following query:

UPDATE table_codes SET used='1', mail_at=NOW(), user='1' WHERE (code='1' OR code='2') AND used='0';

My question is how to prevent that another user get the same 1 or 2 codes of the first user? The 2 codes can only assigned to 1 user.

Users can get 2 tickets for an event. The 2 codes will be send by mail as barcode to scan at the event.

Answer 1

UPDATE table_codes 
   SET used = 1
     , mail_at = NOW()
     , user = 1
 WHERE used = 0 
 ORDER 
    BY RAND() 
 LIMIT 2;