Impala limit 子句
The limit Impala 中的子句用于将结果集的行数限制为所需的数量,即查询的结果集不包含超出指定限制的记录。
语法
以下是语法 Limit Impala 中的子句。
select * from table_name order by id limit numerical_expression;
例子
假设我们有一个名为 顾客 在数据库中 my_db 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 id 的升序排列表中的记录 order by 子句如下图。
[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,你可以将输出的记录数限制为 4,使用 limit 子句如下图。
[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