mysql时间日期相关函数

### 当前日期
mysql> select current_date() from dual;
+----------------+
| current_date() |
+----------------+
| 2023-04-10     |
+----------------+
### 当前时间
mysql> select current_time() from dual;
+----------------+
| current_time() |
+----------------+
| 21:48:24       |
+----------------+
### 当前时间戳
mysql> select current_timestamp() from dual;
+---------------------+
| current_timestamp() |
+---------------------+
| 2023-04-10 21:48:54 |
+---------------------+
### now
mysql> select now() from dual;
+---------------------+
| now()               |
+---------------------+
| 2023-04-10 21:51:25 |
+---------------------+
### 
mysql> select date(now()) from dual;
+-------------+
| date(now()) |
+-------------+
| 2023-04-10  |
+-------------+
### date_add(date ,interval value type) 在date中加日期或时间

### date_sub(date ,interval value type) 在date中减日期或时间

###datediff(date1,date2) 两个日期差（结果是天）

###timediff(date1,date2) 两个时间差(结果是时分秒)

### 上面函数中的type类型可以是 year minute second day hour

### year() month() day()
mysql> select year(now()),month(now()),day(now()) from dual;
+-------------+--------------+------------+
| year(now()) | month(now()) | day(now()) |
+-------------+--------------+------------+
|        2023 |            4 |         10 |
+-------------+--------------+------------+

### unix_timestamp() 返回的是1970-1-1到现在的秒数
mysql> select unix_timestamp() from dual;
+------------------+
| unix_timestamp() |
+------------------+
|       1681135904 |
+------------------+

### from_unixtime() 将时间戳转换为指定格式
mysql> select from_unixtime(unix_timestamp(),'%Y-%m-%d %H:%i:%s') from dual;
+-----------------------------------------------------+
| from_unixtime(unix_timestamp(),'%Y-%m-%d %H:%i:%s') |
+-----------------------------------------------------+
| 2023-04-10 22:16:40                                 |
+-----------------------------------------------------+