Tests done on (rather) old system
Ubuntu 14.04.1 LTS
MySQL Ver 14.14 Distrib 5.5.62
PHP 5.5.9
Storage Engine: InnoDB and MyISAM
> DESC table;
+-------+------------+
| Field | Type |
+-------+------------+
| fs | bigint(20) |
+-------+------------+
- unix timestamp: 1544106294
- timestamp (micro): 1544106294000000
> INSERT INTO table (fs) VALUES (1544106294000000);
-> 1544106294000000
> INSERT INTO table (fs) VALUES (154410629400000012);
-> 154410629400000012
> INSERT INTO table (fs) VALUES (1544106294000000123);
-> 1544106294000000123
> INSERT INTO table (fs) VALUES (15441062940000001234);
-> 9223372036854775807
(2^63-1 = 9223372036854775808)
Time resolution will be micro-seconds.