Impala中的 distinct 运算符用于通过删除重复项来获取唯一值.
关注是 distinct 运算符的语法.
select distinct columns… from table_name;
假设我们在Impala中有一个名为 customers 的表及其内容如下 :
[quickstart.cloudera:21000] > select distinct id, name, age, salary from customers; Query: select distinct id, name, age, salary from customers
在这里您可以观察客户Ramesh和Chaitali输入两次的工资,并使用 distinct 运算符,我们可以选择如下所示的唯一值.
[quickstart.cloudera:21000] > select distinct name, age, address from customers;
执行时,上面的查询给出以下输出.
Query: select distinct id, name from customers +----------+-----+-----------+ | name | age | address | +----------+-----+-----------+ | Ramesh | 32 | Ahmedabad | | Khilan | 25 | Delhi | | kaushik | 23 | Kota | | Chaitali | 25 | Mumbai | | Hardik | 27 | Bhopal | | Komal | 22 | MP | +----------+-----+-----------+ Fetched 9 row(s) in 1.46s