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)
