将TIME(N)和DATETIME(N)值转换为数字形式可以通过将0(+0)添加到它们来完成。以下是此类转换的规则 −
转换为整数
当N为0时，TIME(N)和DATETIME(N)值将被转换为整数。
例如，CURTIME()和NOW()的值可以按如下方式转换为整数值 −
mysql> SELECT CURTIME(), CURTIME()+0;
+-----------+-------------------+
| CURTIME() | CURTIME()+0 |
+-----------+-------------------+
| 19:42:54 | 194254 |
+-----------+-------------------+
1 row in set (0.04 sec)
mysql> SELECT NOW(), NOW()+0;
+-------------------------+----------------------------------+
| NOW() | NOW()+0 |
+-------------------------+----------------------------------+
| 2017-10-27 19:43:43 | 20171027194343 |
+-------------------------+----------------------------------+
1 row in set (0.00 sec)转换为 DECIMAL
当 N 大于 0 时，TIME(N) 和 DATETIME(N) 值将转换为整数。
例如，CURTIME() 和 NOW() 的值可以转换为十进制值，如下 -
mysql> SELECT CURTIME(), CURTIME(3)+0;
+-----------+-------------------+
| CURTIME() | CURTIME()+0 |
+-----------+-------------------+
| 19:47:40 | 194740.575 |
+-----------+-------------------+
1 row in set (0.04 sec)
mysql> SELECT NOW(), NOW(3)+0;
+-------------------------+----------------------------------+
| NOW() | NOW()+0 |
+-------------------------+----------------------------------+
| 2017-10-27 19:48:45 | 20171027194845.589 |
+-------------------------+----------------------------------+
1 row in set (0.00 sec)
