Impala - Having 子句

Impala 中的 Having 子句使您能够指定条件来过滤哪些组结果出现在最终结果中。

一般来说,Having子句与group by子句一起使用; 它对 GROUP BY 子句创建的组设置条件。

语法

以下是 Having 子句的语法。

select * from table_name ORDER BY col_name [ASC|DESC] [NULLS FIRST|NULLS LAST]

示例

假设数据库my_db中有一个名为customers的表,其内容如下 −

[quickstart.cloudera:21000] > select * from customers; 
Query: select * from customers 
+----+----------+-----+-------------+--------+ 
| 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  | 
| 7  | ram      | 25  | chennai     | 23000  | 
| 8  | rahim    | 22  | vizag       | 31000  | 
| 9  | robert   | 23  | banglore    | 28000  | 
+----+----------+-----+-----------+--------+ 
Fetched 9 row(s) in 0.51s

以下是在 Impala 中使用 Having 子句的示例 −

[quickstart.cloudera:21000] > select max(salary) from customers group by age having max(salary) > 20000;

此查询最初按年龄对表进行分组,并选择每组的最高薪水并显示这些薪水,这些薪水大于 20000,如下所示。

20000 
+-------------+ 
| max(salary) |
+-------------+ 
| 30000       |
| 35000       | 
| 40000       | 
| 32000       | 
+-------------+ 
Fetched 4 row(s) in 1.30s