How to make a unique datetime without seconds? I need to build a table accepting one row for each minute. If I set the type of primary key to datetime, 60 records can be added for each minute.

Is there any trick to design a table to keep 0000-00-00 00:00 unique?
Store CONCAT(LEFT(NOW(), 16), ':00') into the PRIMARY KEY that is a DATETIME.

mysql&gt; SELECT NOW(), CONCAT(LEFT(NOW(), 16), ':00');
+---------------------+--------------------------------+
| NOW()               | CONCAT(LEFT(NOW(), 16), ':00') |
+---------------------+--------------------------------+
| 2015-12-11 21:37:38 | 2015-12-11 21:37:00            |
+---------------------+--------------------------------+