How to Split a table rows into fixed size chunk in Oracle

问题

I have a large table 1 million+ rows with a numeric column as primary key. I was trying for an Oracle sql query to get a split of size say 500. So that I have sort of buckets that have 500 records each and give their max and min value in that bucket. sample data

pk_column column1 column2 column3
1002      abcd    1234    15-apr-20
1004      efgh    3435    14-apr-20
1007      ijkl    8855    16-apr-20
....
....
....
2002      asdf    8565    17-apr-20
2005      efgh    5894    14-apr-20   

the desired output is something like below

bucket_no no_of_element min_value max_value
1         500           1002      2002
2         500           2005      3002
3         500           3003      4002
4         480           4003      4500

The code that I could come up with using NTILE or WIDTH_BUCKET is not able to decide the number of bucket size so that no of element is kind of fixed. As the number of elements keep changing , I am unable to find a way to calculate the bucket count dynamically and use it in the NTILE or WIDTH_BUCKET window function. Use of LEAD and LAG function in a hierarchical way was a lot confusing. Could anyone suggest how to tackle this.

回答1:

You can use the analytical function ROW_NUMBER as follows:

SELECT
    RN   AS BUCKET_NO,
    COUNT(1) AS NO_OF_ELEMENT,
    MIN(PK_COLUMN) AS MIN_VALUE,
    MAX(PK_COLUMN) AS MAX_VALUE
FROM
    ( SELECT T.*,
            MOD(ROW_NUMBER() OVER(ORDER BY PK_COLUMN) - 1, 500) + 1 RN
        FROM YOUR_TABL T
    )
GROUP BY RN

来源：https://stackoverflow.com/questions/61229208/how-to-split-a-table-rows-into-fixed-size-chunk-in-oracle