mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2020-06-09 23:21:10 |
+---------------------+
1 row in set (0.00 sec)

mysql> select curdate();
+------------+
| curdate()  |
+------------+
| 2020-06-09 |
+------------+
1 row in set (0.00 sec)

mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| 23:21:23  |
+-----------+
1 row in set (0.00 sec)

mysql> select year(now());
+-------------+
| year(now()) |
+-------------+
|        2020 |
+-------------+
1 row in set (0.00 sec)

mysql> select month(now());
+--------------+
| month(now()) |
+--------------+
|            6 |
+--------------+
1 row in set (0.00 sec)

mysql> select day(now());
+------------+
| day(now()) |
+------------+
|          9 |
+------------+
1 row in set (0.00 sec)

mysql> select hour(now());
+-------------+
| hour(now()) |
+-------------+
|          23 |
+-------------+
1 row in set (0.00 sec)

mysql> select minute(now());
+---------------+
| minute(now()) |
+---------------+
|            24 |
+---------------+
1 row in set (0.00 sec)

mysql> select second(now());
+---------------+
| second(now()) |
+---------------+
|            32 |
+---------------+
1 row in set (0.00 sec)

案例：

mysql> select (year(now())-year(‘1998-01-01 00:01:01‘));
+-------------------------------------------+
| (year(now())-year(‘1998-01-01 00:01:01‘)) |
+-------------------------------------------+
|                                        22 |
+-------------------------------------------+
1 row in set (0.00 sec)

mysql> select (year(‘1998-01-01 00:01:01‘));
+-------------------------------+
| (year(‘1998-01-01 00:01:01‘)) |
+-------------------------------+
|                          1998 |
+-------------------------------+
1 row in set (0.00 sec)

mysql> select str_to_date();

mysql> select str_to_date(‘1-1 2020‘,‘%m-%d %y‘);
+------------------------------------+
| str_to_date(‘1-1 2020‘,‘%m-%d %y‘) |
+------------------------------------+
| 2020-01-01                         |
+------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select date_format(now(),‘%Y-%m-%d‘);
+-------------------------------+
| date_format(now(),‘%Y-%m-%d‘) |
+-------------------------------+
| 2020-06-09                    |
+-------------------------------+
1 row in set (0.00 sec)