sql中interval用法总结

interval作为函数时

当interval作为一个函数时，它被当做一个比较函数，即interval()，如interval(4,0,1,2,3,4,5,6)，则在函数中，第一个数4作为被比较数，后面的0,1,2,3,4,5,6为比较数，然后将后面的数字依次与4进行比较，返回小于等于4的个数，所以上述结果为5，注意，只有将4后面的数字从小到大进行排列，interval函数才能正常使用，若排序混乱，可以使用，但会影响最终结果。

interval作为关键字时

当interval作为一个关键字时，表示为时间间隔，常用在date_add()、date_sub()函数中，常用于时间的加减法。

时间的加法

使用date_add函数时

mysql> select date_add('2020-07-20', interval +1 day);                 
+-----------------------------------------+
| date_add('2020-07-20', interval +1 day) |
+-----------------------------------------+
| 2020-07-21                              |
+-----------------------------------------+
1 row in set (0.01 sec)

mysql> select date_add('2020-07-20', interval +1 hour);
+------------------------------------------+
| date_add('2020-07-20', interval +1 hour) |
+------------------------------------------+
| 2020-07-20 01:00:00                      |
+------------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add('2020-07-20', interval +1 minute);
+--------------------------------------------+
| date_add('2020-07-20', interval +1 minute) |
+--------------------------------------------+
| 2020-07-20 00:01:00                        |
+--------------------------------------------+
1 row in set (0.00 sec)123456789101112131415161718192021222324

使用DATE关键字时，需要确定时间的粒度大小，再进行具体时刻的选取，可供选择的时间粒度如下

MICROSECOND
SECOND
MINUTE
HOUR
DAY
WEEK
MONTH
QUARTER
YEAR
SECOND_MICROSECOND
MINUTE_MICROSECOND
MINUTE_SECOND
HOUR_MICROSECOND
HOUR_SECOND
HOUR_MINUTE
DAY_MICROSECOND
DAY_SECOND
DAY_MINUTE
DAY_HOUR
YEAR_MONTH

使用如下

mysql>  select DATE '2020-07-20' + interval '1 31' hour_second;
+-------------------------------------------------+
| DATE '2020-07-20' + interval '1 31' hour_second |
+-------------------------------------------------+
| 2020-07-20 00:01:31                             |
+-------------------------------------------------+
1 row in set (0.00 sec)

mysql>  select DATE '2020-07-20' + interval '2' microsecond;
+----------------------------------------------+
| DATE '2020-07-20' + interval '2' microsecond |
+----------------------------------------------+
| 2020-07-20 00:00:00.000002                   |
+----------------------------------------------+
1 row in set (0.00 sec)123456789101112131415

时间的减法

与时间的加法使用方式一致，将 + 号换成 - 号就可以

mysql> select date_add('2020-07-20', interval -1 day); 
+-----------------------------------------+
| date_add('2020-07-20', interval -1 day) |
+-----------------------------------------+
| 2020-07-19                              |
+-----------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add('2020-07-20', interval -1 hour); 
+------------------------------------------+
| date_add('2020-07-20', interval -1 hour) |
+------------------------------------------+
| 2020-07-19 23:00:00                      |
+------------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add('2020-07-20', interval -1 minute); 
+--------------------------------------------+
| date_add('2020-07-20', interval -1 minute) |
+--------------------------------------------+
| 2020-07-19 23:59:00                        |
+--------------------------------------------+
1 row in set (0.00 sec)

-----------------

mysql>  select DATE '2020-07-20' - interval '1 31' hour_second; 
+-------------------------------------------------+
| DATE '2020-07-20' - interval '1 31' hour_second |
+-------------------------------------------------+
| 2020-07-19 23:58:29                             |
+-------------------------------------------------+
1 row in set (0.00 sec)

mysql>  select DATE '2020-07-20' - interval '2' microsecond;  
+----------------------------------------------+
| DATE '2020-07-20' - interval '2' microsecond |
+----------------------------------------------+
| 2020-07-19 23:59:59.999998                   |
+----------------------------------------------+
1 row in set (0.00 sec)