Impala - 联合条款

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您可以使用 Impala 的Union子句组合两个查询的结果。

句法

以下是 Impala 中Union子句的语法。

query1 union query2;

例子

假设数据库my_db中有一个名为customer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  | 
| 9  | robert   | 23  | banglore  | 28000  | 
| 2  | Khilan   | 25  | Delhi     | 15000  | 
| 4  | Chaitali | 25  | Mumbai    | 35000  | 
| 7  | ram      | 25  | chennai   | 23000  | 
| 6  | Komal    | 22  | MP        | 32000  | 
| 8  | ram      | 22  | vizag     | 31000  | 
| 5  | Hardik   | 27  | Bhopal    | 40000  | 
| 3  | kaushik  | 23  | Kota      | 30000  | 
+----+----------+-----+-----------+--------+ 
Fetched 9 row(s) in 0.59s

同样，假设我们有另一个表名为employee，其内容如下：

[quickstart.cloudera:21000] > select * from employee; 
Query: select * from employee 
+----+---------+-----+---------+--------+ 
| id | name    | age | address | salary | 
+----+---------+-----+---------+--------+ 
| 3  | mahesh  | 54  | Chennai | 55000  | 
| 2  | ramesh  | 44  | Chennai | 50000  | 
| 4  | Rupesh  | 64  | Delhi   | 60000  | 
| 1  | subhash | 34  | Delhi   | 40000  | 
+----+---------+-----+---------+--------+ 
Fetched 4 row(s) in 0.59s

以下是 Impala 中union子句的示例。在此示例中，我们按照 id 的顺序排列两个表中的记录，并使用两个单独的查询并使用 UNION 子句连接这些查询，将记录数量限制为3。

[quickstart.cloudera:21000] > select * from customers order by id limit 3
 union select * from employee order by id limit 3;

执行时，上述查询给出以下输出。

Query: select * from customers order by id limit 3 union select 
   * from employee order by id limit 3 
+----+---------+-----+-----------+--------+ 
| id | name    | age | address   | salary | 
+----+---------+-----+-----------+--------+ 
| 2  | Khilan  | 25  | Delhi     | 15000  |
| 3  | mahesh  | 54  | Chennai   | 55000  | 
| 1  | subhash | 34  | Delhi     | 40000  | 
| 2  | ramesh  | 44  | Chennai   | 50000  | 
| 3  | kaushik | 23  | Kota      | 30000  | 
| 1  | Ramesh  | 32  | Ahmedabad | 20000  | 
+----+---------+-----+-----------+--------+ 
Fetched 6 row(s) in 3.11s