mysql ORDER BY的使用

新建表如下：

+----+---------------------+------+----------+
| id | sale_date           | num  | order_id |
+----+---------------------+------+----------+
|  1 | 2020-05-12 23:23:12 |   12 |      100 |
|  2 | 2020-05-14 23:23:31 |   15 |      100 |
|  3 | 2020-05-15 23:23:50 |    1 |      100 |
|  4 | 2020-05-16 23:24:14 |   10 |      101 |
|  5 | 2020-05-17 23:24:33 | NULL |      101 |
+----+---------------------+------+----------+

一 按order_id列默认排序查询：

mysql> SELECT * FROM order_sale_info ORDER BY order_sale_info.order_id;
+----+---------------------+------+----------+
| id | sale_date           | num  | order_id |
+----+---------------------+------+----------+
|  1 | 2020-05-12 23:23:12 |   12 |      100 |
|  2 | 2020-05-14 23:23:31 |   15 |      100 |
|  3 | 2020-05-15 23:23:50 |    1 |      100 |
|  4 | 2020-05-16 23:24:14 |   10 |      101 |
|  5 | 2020-05-17 23:24:33 | NULL |      101 |
+----+---------------------+------+----------+
5 rows in set

可以看到按order_id列查询时默认按升序排列，与添加ASC关键字效果一致。

mysql> SELECT * FROM order_sale_info ORDER BY order_sale_info.order_id ASC;
+----+---------------------+------+----------+
| id | sale_date           | num  | order_id |
+----+---------------------+------+----------+
|  1 | 2020-05-12 23:23:12 |   12 |      100 |
|  2 | 2020-05-14 23:23:31 |   15 |      100 |
|  3 | 2020-05-15 23:23:50 |    1 |      100 |
|  4 | 2020-05-16 23:24:14 |   10 |      101 |
|  5 | 2020-05-17 23:24:33 | NULL |      101 |
+----+---------------------+------+----------+
5 rows in set

二 多列排序查询：

按order_id 升序，num升序排序效果，每个排序字段后边要跟排序的类型（ASC或者DESC），如果排序类型为ASC可以不写，默认为ASC，如上述一情况。

mysql> SELECT * FROM order_sale_info ORDER BY order_sale_info.order_id ASC,order_sale_info.num ASC;
+----+---------------------+------+----------+
| id | sale_date           | num  | order_id |
+----+---------------------+------+----------+
|  3 | 2020-05-15 23:23:50 |    1 |      100 |
|  1 | 2020-05-12 23:23:12 |   12 |      100 |
|  2 | 2020-05-14 23:23:31 |   15 |      100 |
|  5 | 2020-05-17 23:24:33 | NULL |      101 |
|  4 | 2020-05-16 23:24:14 |   10 |      101 |
+----+---------------------+------+----------+
5 rows in set

按order_id 升序，num降序排序效果，每个排序字段后边要跟排序的类型（ASC或者DESC）。

mysql> SELECT * FROM order_sale_info ORDER BY order_sale_info.order_id ASC,order_sale_info.num DESC;
+----+---------------------+------+----------+
| id | sale_date           | num  | order_id |
+----+---------------------+------+----------+
|  2 | 2020-05-14 23:23:31 |   15 |      100 |
|  1 | 2020-05-12 23:23:12 |   12 |      100 |
|  3 | 2020-05-15 23:23:50 |    1 |      100 |
|  4 | 2020-05-16 23:24:14 |   10 |      101 |
|  5 | 2020-05-17 23:24:33 | NULL |      101 |
+----+---------------------+------+----------+
5 rows in set

如果不写排序类型，默认为升序，如下：

mysql> SELECT * FROM order_sale_info ORDER BY order_sale_info.order_id,order_sale_info.num DESC;
+----+---------------------+------+----------+
| id | sale_date           | num  | order_id |
+----+---------------------+------+----------+
|  2 | 2020-05-14 23:23:31 |   15 |      100 |
|  1 | 2020-05-12 23:23:12 |   12 |      100 |
|  3 | 2020-05-15 23:23:50 |    1 |      100 |
|  4 | 2020-05-16 23:24:14 |   10 |      101 |
|  5 | 2020-05-17 23:24:33 | NULL |      101 |
+----+---------------------+------+----------+
5 rows in set

order_id列未声明排序类型，默认为升序，num声明排序规则未DESC，体现为降序。