Impala - OFFSET 子句

一般情况下，select 查询结果集中的行从 0 开始。使用offset子句，我们可以决定从哪里开始考虑输出。例如，如果我们将偏移量选择为 0，结果将和往常一样；如果我们将偏移量选择为 5，则结果从第五行开始。

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limit和order by子句按其 ID 的升序排列表中的记录，并将记录数限制为 4，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子句的一个示例。在这里，我们按其 ID 的顺序获取customers表中的记录，并从第 0 行开始打印前四行。

[quickstart.cloudera:21000] > select * from customers order by id limit 4 offset 0;

执行上述查询后，将得到以下结果。

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，您可以从偏移量为 5 的行开始，从customers表中获取四条记录，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