Is C in days? Weeks? What?
One syntax in MySQL for adding 3 days is
+ INTERVAL 3 DAY
mysql> SELECT MAX(ts), MAX(ts) + INTERVAL 3 DAY FROM ts;
+---------------------+--------------------------+
| MAX(ts) | MAX(ts) + INTERVAL 3 DAY |
+---------------------+--------------------------+
| 2011-12-05 19:07:29 | 2011-12-08 19:07:29 |
+---------------------+--------------------------+
+---------------+--------------------------------+
| MAX(DATE(ts)) | MAX(DATE(ts)) + INTERVAL 3 DAY |
+---------------+--------------------------------+
| 2011-12-05 | 2011-12-08 |
+---------------+--------------------------------+
+---------------+--------------------------------+
| MAX(DATE(ts)) | MAX(DATE(ts) + INTERVAL 3 DAY) |
+---------------+--------------------------------+
| 2011-12-05 | 2011-12-08 |
+---------------+--------------------------------+
+---------------+--------------------------------+
| MAX(DATE(ts)) | MAX(DATE(ts + INTERVAL 3 DAY)) |
+---------------+--------------------------------+
| 2011-12-05 | 2011-12-08 |
+---------------+--------------------------------+
mysql> SHOW CREATE TABLE ts\G
*************************** 1. row ***************************
Table: ts
Create Table: CREATE TABLE `ts` (
`ts` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
KEY `ts1` (`ts`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
TIMESTAMP, DATE, and DATETIME all work similarly in this context.
"DAY" can be replaced by any of YEAR, MONTH, HOUR, MINUTE, SECOND.