Impala offset
通常,
select 查询的结果集中的行从 0 开始。使用
offset 子句,我们可以决定应该从哪里考虑输出。例如,如果我们选择偏移量为0,结果将照常;如果我们选择偏移量为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id的升序排列表中的记录并将记录数限制为4条,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 子句的示例。在这里,我们按照 id 的顺序获取
customers 表中的记录,并从第 0
th 行开始打印前四行。
[quickstart.cloudera:21000] > select * from customers order by id limit 4 offset 0;
执行时,上述查询给出以下结果。
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
customers 表中从偏移量为 5 的行开始获取 4 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