Impala 简明教程
Impala - Limit Clause
Impala 中的 limit 子句用于将结果集的行数限制为所需数量，即，查询结果集不再持有超出行数限制的记录。
Example
假设数据库 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你可以使用 order by 子句按其 id 的升序排列表格中的记录，如下所示。
[quickstart.cloudera:21000] > select * from customers order by id;
Query: select * from customers order by id
+----+----------+-----+-----------+--------+
| 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 |
| 5 | Hardik | 27 | Bhopal | 40000 |
| 6 | Komal | 22 | MP | 32000 |
| 7 | ram | 25 | chennai | 23000 |
| 8 | ram | 22 | vizag | 31000 |
| 9 | robert | 23 | banglore | 28000 |
+----+----------+-----+-----------+--------+
Fetched 9 row(s) in 0.54s现在，你可以使用 limit 子句限制输出记录的数量为 4，使用 limit 子句，如下所示。
[quickstart.cloudera:21000] > select * from customers order by id limit 4;在执行后，上述查询给出以下输出。
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