ORDER BY

ORDER BY 语法用于根据 SELECT 语句中的一个或多个列对数据进行升序或降序排序。

Syntax

ORDER BY 的基本语法如下：

sql

SELECT column1, column2, ...
FROM table_name
ORDER BY column1 [ASC | DESC], column2 [ASC | DESC], ...;

ORDER BY 可以用于一个或多个列。ASC 关键字用于升序排序（默认），DESC 关键字用于降序排序。

示例

假如我们有一个名为 system_metrics 的表：

sql

+-------+-------+----------+-------------+-----------+---------------------+
| host  | idc   | cpu_util | memory_util | disk_util | ts                  |
+-------+-------+----------+-------------+-----------+---------------------+
| host1 | idc_a |     11.8 |        10.3 |      10.3 | 2022-11-03 03:39:57 |
| host1 | idc_b |       50 |        66.7 |      40.6 | 2022-11-03 03:39:57 |
| host1 | idc_c |     50.1 |        66.8 |      40.8 | 2022-11-03 03:39:57 |
| host1 | idc_e |     NULL |        66.7 |      40.6 | 2022-11-03 03:39:57 |
| host2 | idc_a |     80.1 |        70.3 |        90 | 2022-11-03 03:39:57 |
+-------+-------+----------+-------------+-----------+---------------------+

要根据 memory_util 列对数据进行升序排序，可以使用以下 SQL 语句：

sql

SELECT * FROM system_metrics
ORDER BY memory_util ASC;

结果为：

sql

+-------+-------+----------+-------------+-----------+---------------------+
| host  | idc   | cpu_util | memory_util | disk_util | ts                  |
+-------+-------+----------+-------------+-----------+---------------------+
| host1 | idc_a |     11.8 |        10.3 |      10.3 | 2022-11-03 03:39:57 |
| host1 | idc_b |       50 |        66.7 |      40.6 | 2022-11-03 03:39:57 |
| host1 | idc_e |     NULL |        66.7 |      40.6 | 2022-11-03 03:39:57 |
| host1 | idc_c |     50.1 |        66.8 |      40.8 | 2022-11-03 03:39:57 |
| host2 | idc_a |     80.1 |        70.3 |        90 | 2022-11-03 03:39:57 |
+-------+-------+----------+-------------+-----------+---------------------+

要根据 disk_util 列对数据进行降序排序，可以使用以下 SQL 语句：

sql

SELECT * FROM system_metrics
ORDER BY disk_util DESC;

结果为：

sql

+-------+-------+----------+-------------+-----------+---------------------+
| host  | idc   | cpu_util | memory_util | disk_util | ts                  |
+-------+-------+----------+-------------+-----------+---------------------+
| host2 | idc_a |     80.1 |        70.3 |        90 | 2022-11-03 03:39:57 |
| host1 | idc_c |     50.1 |        66.8 |      40.8 | 2022-11-03 03:39:57 |
| host1 | idc_b |       50 |        66.7 |      40.6 | 2022-11-03 03:39:57 |
| host1 | idc_e |     NULL |        66.7 |      40.6 | 2022-11-03 03:39:57 |
| host1 | idc_a |     11.8 |        10.3 |      10.3 | 2022-11-03 03:39:57 |
+-------+-------+----------+-------------+-----------+---------------------+