Shulou(Shulou.com)05/31 Report--

Today, I will talk to you about how to understand the keep function, many people may not know much about it. In order to make you understand better, the editor has summarized the following for you. I hope you can get something according to this article.

Keep function

Example:

SELECT TO_CHAR (log_date, 'YYYY') year

TO_CHAR (log_date,'Q') quarter

TO_CHAR (log_date, 'MM') month

Employee_id

MIN (old_salary) keep (dense_rank first order by log_date)

MIN (new_salary) keep (dense_rank last order by log_date)

GROUPING_ID (TO_CHAR (log_date, 'YYYY')

TO_CHAR (log_date,'Q')

TO_CHAR (log_date, 'MM'))

Gid

FROM plch_emp_log

GROUP BY ROLLUP (TO_CHAR (log_date, 'YYYY')

TO_CHAR (log_date,'Q')

TO_CHAR (log_date, 'MM'))

Employee_id

-group by grouping

-dense (dense) sorting is performed within each group according to log_date. The sorted result first takes the first row and last takes the last row.

-then perform the min aggregate function on the extracted result

* several kinds of sorting

ROW_NUMBER () is a sort with no duplicate values (even if the two records are the same, the sequence numbers are not repeated) and will not have the same rank.

DENSE_RANK () is a sequential sort, with two second places still following the third place.

RANK () is the jump sort, and the second place is the fourth place.

After reading the above, do you have any further understanding of how to understand the keep function? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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