If the date, item, and category are the same in the table, I’d like to treat it as the same row and return n rows out of them(ex: if n is 3, then limit 0, 3).
------------------------------------------
id | date | item | category |
------------------------------------------
101 | 20220201| pencil | stationery | <---
------------------------------------------ | treat as same result
105 | 20220201| pencil | stationery | <---
------------------------------------------
120 | 20220214| desk | furniture |
------------------------------------------
125 | 20220219| tongs | utensil | <---
------------------------------------------ | treat as same
129 | 20220219| tongs | utensil | <---
------------------------------------------
130 | 20220222| tongs | utensil |
expected results (if n is 3)
-----------------------------------------------
id | date | item | category | rank
-----------------------------------------------
101 | 20220201| pencil | stationery | 1
-----------------------------------------------
105 | 20220201| pencil | stationery | 1
-----------------------------------------------
120 | 20220214| desk | furniture | 2
-----------------------------------------------
125 | 20220219| tongs | utensil | 3
-----------------------------------------------
129 | 20220219| tongs | utensil | 3
The problem is that I have to bring the values of each group as well. If I have only one column to group by, I can compare id value with origin table, but I don’t know what to do with multiple columns.
Is there any way to solve this problem?
For reference, I used a user variable to compare it with previous values, I couldn’t use it because the duration was slow.
SELECT
*,
IF(@prev_date=date and @prev_item=item and @prev_category=category,@ranking, @ranking:=@ranking+1) AS sameRow,
@prev_item:=item,
@prev_date:= date,
@prev_category:=category,
@ranking
FROM ( SELECT
I’m using Mysql 8.0 version and id value is not a continuous number because I have to order by before group by.
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Answer
if I understand correctly, you can try to use dense_rank
window function and set order by
with your expected columns
if date
column can represent the order number I would put it first.
SELECT *
FROM (
SELECT *,dense_rank() OVER(ORDER BY date, item, category) rnk
FROM T
) t1