mysql 时间

显示当前时间：

mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2016-12-27 23:42:25 |
+---------------------+
1 row in set (0.00 sec)

mysql> SELECT CURRENT_TIMESTAMP;
+---------------------+
| CURRENT_TIMESTAMP   |
+---------------------+
| 2016-12-27 23:41:08 |
+---------------------+
1 row in set (0.00 sec)

以秒形式显示当前时间：

mysql> select UNIX_TIMESTAMP();
+------------------+
| UNIX_TIMESTAMP() |
+------------------+
|       1482853439 |
+------------------+
1 row in set (0.00 sec)

精确到毫秒：

mysql> SELECT ROUND(UNIX_TIMESTAMP(CURTIME(4)) * 1000);
+------------------------------------------+
| ROUND(UNIX_TIMESTAMP(CURTIME(4)) * 1000) |
+------------------------------------------+
|                            1482853561290 |
+------------------------------------------+
1 row in set (0.02 sec)

mysql在5.6.4版本之前会将秒之后的时间截取掉，也就是最高精度只到秒。5.6.4及之后的版本支持到微秒（2010-12-10 14:12:09.019473，小数点后6位）。不过创建表时需要指定精度，指定小数点后存储几位：

CREATE TABLE t1 (t TIME(3), dt DATETIME(6));

例如：

mysql> CREATE TABLE fractest( c1 TIME(2), c2 DATETIME(2), c3 TIMESTAMP(2) );
Query OK, 0 rows affected (0.61 sec)

mysql> INSERT INTO fractest VALUES ('17:51:04.777', '2016-10-10 17:51:04.777', '2016-10-10 17:51:04.777');
Query OK, 1 row affected (0.05 sec)

mysql> SELECT * FROM fractest;
+-------------+------------------------+------------------------+
| c1          | c2                     | c3                     |
+-------------+------------------------+------------------------+
| 17:51:04.78 | 2016-10-10 17:51:04.78 | 2016-10-10 17:51:04.78 |
+-------------+------------------------+------------------------+
1 row in set (0.00 sec)