row_number() over (partition by nf order by cs desc)<= 50
时间: 2023-10-27 20:52:25 浏览: 92
This SQL code is using the window function `row_number()` to assign a unique ranking number to each row within a partition of the result set. The partition is defined by the value of the column "nf", and the rows within each partition are ordered by the value of the column "cs" in descending order.
The code is then using a filter condition to limit the result set to only those rows where the ranking number is less than or equal to 50. In other words, it is selecting the top 50 rows within each partition based on the value of "cs".
Overall, this code is useful for ranking and selecting the top results within each group of data based on a specific column value.
相关问题
row_number() over (partition by nf order by cs desc)
This SQL expression uses the window function "row_number()" to assign a unique row number to each row within a partition defined by the "nf" column. The rows within each partition are further ordered by the "cs" column in descending order.
For example, if we have a table with columns "nf" and "cs" and the following data:
nf | cs
---|---
A | 10
A | 20
B | 15
B | 5
The expression "row_number() over (partition by nf order by cs desc)" would produce the following result:
nf | cs | row_number
---|---|-----------
A | 20 | 1
A | 10 | 2
B | 15 | 1
B | 5 | 2
Note that within each partition (A and B), the rows are ordered by descending "cs" values and assigned a row number accordingly. The row number starts from 1 for each partition.
hive中row_number over(partition by order by)
`row_number() over(partition by order by)`是Hive中的窗口函数,用于对查询结果进行分组和排序,并为每个分组中的行分配一个唯一的序号。其中,`partition by`用于指定分组的列,`order by`用于指定排序的列。
以下是一个示例,假设我们有一个名为`tmp_learning_mary`的表,其中包含`id`和`score`两列数据。我们想要按照`id`分组,并按照`score`从高到低排序,为每个分组中的行分配一个唯一的序号。可以使用以下语句:
```sql
select *, row_number() over(partition by id order by score desc) as ranking from tmp_learning_mary;
```
这将返回一个结果集,其中包含原始表中的所有列,以及一个名为`ranking`的新列,其中包含每个分组中的行的唯一序号。
如果我们想要在每个分组中随机选择一行,并为其分配一个唯一的序号,可以使用以下语句:
```sql
select * from (select *, row_number() over(partition by id order by rand()) as ranking from tmp_learning_mary) t where t.ranking = 1;
```
这将返回一个结果集,其中包含原始表中的所有列,以及一个名为`ranking`的新列,其中包含每个分组中随机选择的行的唯一序号。
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