Impala教程

Impala offset

通常, select 查询的结果集中的行从 0 开始。使用 offset 子句,我们可以决定应该从哪里考虑输出。例如,如果我们选择偏移量为0,结果将照常;如果我们选择偏移量为5,则结果从第五行开始。
偏移条款

语法

以下是 Impala 中 offset 子句的语法。
select data from table_name Group BY col_name;

示例

假设我们在数据库 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 | 
+----+----------+-----+-----------+--------+ 
| 3  | kaushik  | 23 | Kota      | 30000  | 
| 6  | Komal    | 22 | MP        | 32000  | 
| 1  | Ramesh   | 32  | Ahmedabad | 20000  | 
| 5  | Hardik   | 27  | Bhopal    | 40000  | 
| 2  | Khilan   | 25 | Delhi     | 15000  | 
| 8  | ram      | 22  | vizag     | 31000  | 
| 9  | robert   | 23  | banglore  | 28000  |
| 7  | ram      | 25  | chennai   | 23000  | 
| 4  | Chaitali | 25  | Mumbai    | 35000  | 
+----+----------+-----+-----------+--------+ 
Fetched 9 row(s) in 0.51s
您可以使用 limitorder by子句按id的升序排列表中的记录并将记录数限制为4条,如下所示.
Query: select * from customers order by id limit 4 
+----+----------+-----+-----------+--------+ 
| 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  | 
+----+----------+-----+-----------+--------+ 
Fetched 4 row(s) in 0.64s
以下是 offset 子句的示例。在这里,我们按照 id 的顺序获取 customers 表中的记录,并从第 0 th 行开始打印前四行。
[quickstart.cloudera:21000] > select * from customers order by id limit 4 offset 0;
执行时,上述查询给出以下结果。
Query: select * from customers order by id limit 4 offset 0 
+----+----------+-----+-----------+--------+
| 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  | 
+----+----------+-----+-----------+--------+ 
Fetched 4 row(s) in 0.62s
同样,您可以从 customers 表中从偏移量为 5 的行开始获取 4 条记录,如下所示。
[quickstart.cloudera:21000] > select * from customers order by id limit 4 offset 5; 
Query: select * from customers order by id limit 4 offset 5 
+----+--------+-----+----------+--------+ 
| id | name   | age | address  | salary | 
+----+--------+-----+----------+--------+ 
| 6  | Komal  | 22 | MP       | 32000  | 
| 7  | ram    | 25  | chennai  | 23000  | 
| 8  | ram    | 22  | vizag    | 31000  |
| 9  | robert | 23  | banglore | 28000  | 
+----+--------+-----+----------+--------+ 
Fetched 4 row(s) in 0.52s
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