mysql從5.6開始，時間有了更高的精度：秒支持到小數點後6位。
[DB152](root@localhost) [test]> SELECT now(6), sysdate(6), CURRENT_TIMESTAMP(6);
+----------------------------+----------------------------+----------------------------+
| now(6) | sysdate(6) | CURRENT_TIMESTAMP(6) |
+----------------------------+----------------------------+----------------------------+
| 2014-01-22 13:58:48.141652 | 2014-01-22 13:58:48.141652 | 2014-01-22 13:58:48.141652 |
+----------------------------+----------------------------+----------------------------+
不加參數的話，不顯示小數點後面的部分，這樣就可以和舊版本的mysql兼容，另外也可以自己指定精確到小數點後幾位:
[DB152](root@localhost) [test]> SELECT now(3), sysdate(), CURRENT_TIMESTAMP(0);
+-------------------------+---------------------+----------------------+
| now(3) | sysdate() | CURRENT_TIMESTAMP(0) |
+-------------------------+---------------------+----------------------+
| 2014-01-22 14:00:47.836 | 2014-01-22 14:00:47 | 2014-01-22 14:00:47 |
+-------------------------+---------------------+----------------------+
如果指定大於6的數字，就會報錯：
ERROR 1426 (42000): Too big PRECISION 7 specified FOR COLUMN 'now'. Maximum IS 6.
但是在建表語句中，卻無法在CURRENT_TIMESTAMP中指定精度。
這樣是錯誤的：
CREATE TABLE t1 (
`created_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP(6)
) engine=innodb DEFAULT charset=utf8;
ERROR 1067 (42000): Invalid DEFAULT VALUE FOR 'created_at'
原因在於timestamp類型的字段默認精度為0，但是我們又人工指定了DEFAULT CURRENT_TIMESTAMP(6)，
前後不對應，就會出錯。
解決辦法就是timestamp和CURRENT_TIMESTAMP使用相同的精度：
CREATE TABLE t1 (
`created_at` TIMESTAMP(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6)
) engine=innodb DEFAULT charset=utf8;
[DB152](root@localhost) [test]> INSERT INTO t1 VALUES();
Query OK, 1 ROW affected (0.00 sec)
[DB152](root@localhost) [test]> SELECT * FROM t1;
+----------------------------+
| created_at |
+----------------------------+
| 2014-01-22 14:10:05.013561 |
+----------------------------+
1 ROW IN SET (0.00 sec)
寫入的時候，我們也可以再次指定精度，小數位數不足就會用後導0來補全：
[DB152](root@localhost) [test]> INSERT INTO t1 VALUES(CURRENT_TIMESTAMP(3));
Query OK, 1 ROW affected (0.01 sec)
[DB152](root@localhost) [test]> SELECT * FROM t1;
+----------------------------+
| created_at |
+----------------------------+
| 2014-01-22 14:12:01.515000 |
+----------------------------+
2 ROWS IN SET (0.00 sec)
[DB152](root@localhost) [test]> SELECT version();
+------------+
| version() |
+------------+
| 5.6.13-log |
+------------+
1 ROW IN SET (0.01 sec)
如果建表的時候，指定4位精度，寫入時，指定6位精度，那麼就會丟失後面2位精度了~ 周知。
另外, 5.6 , 可以支持多個default current_timestamp字段了:
[DB152](root@localhost) [test]> CREATE TABLE t1 (
-> t INT NOT NULL DEFAULT 0,
-> `created_at` TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) ,
-> `last_op_time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
-> `last_op_time4` TIMESTAMP(4) NOT NULL DEFAULT CURRENT_TIMESTAMP(4) ON UPDATE CURRENT_TIMESTAMP(4)
-> ) engine=innodb DEFAULT charset=utf8;
Query OK, 0 ROWS affected (0.00 sec)
[DB152](root@localhost) [test]>
[DB152](root@localhost) [test]> INSERT INTO t1 SET t=1;
Query OK, 1 ROW affected (0.00 sec)
[DB152](root@localhost) [test]> SELECT * FROM t1;
+---+-------------------------+---------------------+--------------------------+
| t | created_at | last_op_time | last_op_time4 |
+---+-------------------------+---------------------+--------------------------+
| 1 | 2014-01-22 14:24:31.201 | 2014-01-22 14:24:31 | 2014-01-22 14:24:31.2016 |
+---+-------------------------+---------------------+--------------------------+
1 ROW IN SET (0.00 sec)
[DB152](root@localhost) [test]> UPDATE t1 SET t=2;
Query OK, 1 ROW affected (0.00 sec)
ROWS matched: 1 Changed: 1 Warnings: 0
[DB152](root@localhost) [test]> SELECT * FROM t1;
+---+-------------------------+---------------------+--------------------------+
| t | created_at | last_op_time | last_op_time4 |
+---+-------------------------+---------------------+--------------------------+
| 2 | 2014-01-22 14:24:31.201 | 2014-01-22 14:24:47 | 2014-01-22 14:24:47.3286 |
+---+-------------------------+---------------------+--------------------------+
1 ROW IN SET (0.00 sec)
