如果我们尝试仅向 MySQL EXTRACT() 函数提供日期值来提取时间值，会输出什么？

当我们尝试从日期中提取小时值时，EXTRACT() 函数将给出输出 0 并带有警告，如下面给出的示例所示 -

mysql> Select EXTRACT(Hour from '2017-10-20');

+---------------------------------+
| EXTRACT(Hour from '2017-10-20') |
+---------------------------------+
| 0                               |
+---------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> Show Warnings;

+---------+------+----------------------------------------------+
| Level   | Code | Message                                      |
+---------+------+----------------------------------------------+
| Warning | 1292 | Truncated incorrect time value: '2017-10-20' |
+---------+------+----------------------------------------------+
1 row in set (0.00 sec)

现在，当我们尝试从日期中提取分钟值时，EXTRACT() 函数将给出日期中的世纪值作为输出，并带有警告，如下面给出的示例所示 -

mysql> Select EXTRACT(Minute from '2017-10-20');
+-----------------------------------+
| EXTRACT(Minute from '2017-10-20') |
+-----------------------------------+
| 20                                |
+-----------------------------------+
1 row in set, 1 warning (0.00 sec)
mysql> Show Warnings;
+---------+------+----------------------------------------------+
| Level   | Code | Message                                      |
+---------+------+----------------------------------------------+
| Warning | 1292 | Truncated incorrect time value: '2017-10-20' |
+---------+------+----------------------------------------------+
1 row in set (0.00 sec)

现在，当我们尝试从日期中提取秒值时，EXTRACT() 函数将给出年份值作为输出，并带有警告，如下面给出的示例所示 -

mysql> Select Extract(Second from '2017-10-20');

+-----------------------------------+
| Extract(Second from '2017-10-20') |
+-----------------------------------+
| 17                                |
+-----------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> Show Warnings;

+---------+------+----------------------------------------------+
| Level   | Code | Message                                      |
+---------+------+----------------------------------------------+
| Warning | 1292 | Truncated incorrect time value: '2017-10-20' |
+---------+------+----------------------------------------------+
1 row in set (0.00 sec)

尝试从当前日期获取时间值（小时、分钟和秒），即通过在日期位置使用 Curdate() ，我们会得到类似的结果。

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