row_number() over (partition by nf order by cs desc)<= 50
时间: 2023-10-27 09:52:25 浏览: 43
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.
row_number over (partition by a order by b desc)
以下是使用row_number() over(partition by name order by timestamp desc)的示例:
```sql
SELECT *, ROW_NUMBER() OVER(PARTITION BY name ORDER BY timestamp DESC) AS idx
FROM your_table_name;
```
这个示例中,ROW_NUMBER()函数根据name分区,并按照timestamp降序排列,为每个分区中的行分配一个唯一的行号。
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