Impala中的limit子句用于将结果集的行数限制为所需的数，即查询的结果集不包含超过指定限制的记录。
以下是Impala中Limit子句的语法。
| select * from table_name order by id limit numerical_expression; |
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order by子句按照id的升序排列表中的记录，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，使用limit子句，您可以将输出的记录数限制为4，使用limit子句如下所示。
| [quickstart.cloudera:21000] > select * from customers order by id limit 4; |
执行时，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 |
