📅  最后修改于: 2020-11-30 05:04:36             🧑  作者: Mango
Impala ORDER BY子句用于根据一列或多列对数据进行升序或降序排序。默认情况下,某些数据库按升序对查询结果进行排序。
以下是ORDER BY子句的语法。
select * from table_name ORDER BY col_name [ASC|DESC] [NULLS FIRST|NULLS LAST]
您可以分别使用关键字ASC或DESC在表中按升序或降序排列数据。
同样,如果我们使用NULLS FIRST,则表中的所有空值都排列在最上面的行中;如果我们使用NULLS LAST,则包含空值的行将排在最后。
假设我们在数据库my_db中有一个名为客户的表,其内容如下-
[quickstart.cloudera:21000] > select * from customers;
Query: select * from customers
+----+----------+-----+-----------+--------+
| id | name | age | address | salary |
+----+----------+-----+-----------+--------+
| 3 | kaushik | 23 | Kota | 30000 |
| 1 | Ramesh | 32 | Ahmedabad | 20000 |
| 2 | Khilan | 25 | Delhi | 15000 |
| 6 | Komal | 22 | MP | 32000 |
| 4 | Chaitali | 25 | Mumbai | 35000 |
| 5 | Hardik | 27 | Bhopal | 40000 |
+----+----------+-----+-----------+--------+
Fetched 6 row(s) in 0.51s
以下是使用order by子句按客户编号升序排列客户表中数据的示例。
[quickstart.cloudera:21000] > Select * from customers ORDER BY id asc;
执行时,以上查询将产生以下输出。
Query: select * from customers ORDER BY id asc
+----+----------+-----+-----------+--------+
| id | name | age | address | salary |
+----+----------+-----+-----------+--------+
| 1 | Ramesh | 32 | Ahmedabad | 20000 |
| 2 | Khilan | 25 | Delhi | 15000 |
| 3 | kaushik | 23 | Kota | 30000 |
| 4 | Chaitali | 25 | Mumbai | 35000 |
| 5 | Hardik | 27 | Bhopal | 40000 |
| 6 | Komal | 22 | MP | 32000 |
+----+----------+-----+-----------+--------+
Fetched 6 row(s) in 0.56s
以相同的方式,您可以使用order by子句按以下降序排列customer表的数据,如下所示。
[quickstart.cloudera:21000] > Select * from customers ORDER BY id desc;
执行时,以上查询将产生以下输出。
Query: select * from customers ORDER BY id desc
+----+----------+-----+-----------+--------+
| id | name | age | address | salary |
+----+----------+-----+-----------+--------+
| 6 | Komal | 22 | MP | 32000 |
| 5 | Hardik | 27 | Bhopal | 40000 |
| 4 | Chaitali | 25 | Mumbai | 35000 |
| 3 | kaushik | 23 | Kota | 30000 |
| 2 | Khilan | 25 | Delhi | 15000 |
| 1 | Ramesh | 32 | Ahmedabad | 20000 |
+----+----------+-----+-----------+--------+
Fetched 6 row(s) in 0.54s