Impala - OFFSET 子句

一般情況下，select 查詢結果集中的行從 0 開始。使用offset子句，我們可以決定從哪裡開始考慮輸出。例如，如果我們將偏移量選擇為 0，結果將和往常一樣；如果我們將偏移量選擇為 5，則結果從第五行開始。

語法

以下是 Impala 中offset 子句的語法。

select data from table_name Group BY col_name;

示例

假設我們在資料庫my_db中有一個名為customers的表，其內容如下：

[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 的升序排列表中的記錄，並將記錄數限制為 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子句的一個示例。在這裡，我們按其 ID 的順序獲取customers表中的記錄，並從第 0 行開始列印前四行。

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

執行上述查詢後，將得到以下結果。

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

同樣，您可以從偏移量為 5 的行開始，從customers表中獲取四條記錄，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