CODEWITHSUNDEEP
mysqlsqlcountaggregate-functionspercentage
Oksana Karacheva
Oksana Karacheva

Reputation: 33

Calculate percentages of count in SQL relative to the category

I am working in MySQL. Initially I had a table that looks like this:

initial database

My task is to calculate the percentage of bookings that were cancelled for people that were in a long waiting list and for people that had short waiting. After some manipulations I came up with the following code:

SELECT
CASE WHEN days_in_waiting_list > (SELECT AVG(days_in_waiting_list) FROM Bookings) THEN 'Long wait'
ELSE 'Short wait' 
END AS waiting, 
is_canceled, COUNT(*), count(*) * 100.0 / sum(count(*)) over() AS perc_cancelled
FROM Bookings
GROUP BY waiting, is_canceled;

The resulting table:

result

But I want the percentages to be calculated for the category, not the whole table. So that the sum of percentages in Short wait was equal to 100, the same is for Long wait. I want it to be like this:

waiting is_cancelled perc
Short wait 0 0.61
Short wait 1 0.39
Long wait 0 0.32
Long wait 1 0.68

Is there a way to do this? I know that it is possible using over(partition by waiting), but it gives me the error

Error Code: 1054. Unknown column 'waiting' in 'window partition by'

Upvotes: 2

Views: 1423

Answers (4)

Fabian Pijcke
Fabian Pijcke

Reputation: 3210

Creating the table with only the relevant data, and 40 random rows :

CREATE TABLE test (
  id INT AUTO_INCREMENT PRIMARY KEY,
  is_canceled INT DEFAULT FLOOR(RAND() * 2),
  days_in_waiting_list INT DEFAULT FLOOR(RAND() * 100)
);
INSERT INTO test () VALUES (), (), (), (), (), (), (), (), (), ();
INSERT INTO test () VALUES (), (), (), (), (), (), (), (), (), ();
INSERT INTO test () VALUES (), (), (), (), (), (), (), (), (), ();
INSERT INTO test () VALUES (), (), (), (), (), (), (), (), (), ();

Your were really close, just add PARTITION BY waiting:

SELECT
  CASE WHEN days_in_waiting_list > (
    SELECT AVG(days_in_waiting_list)
    FROM test
  ) THEN 'Long' ELSE 'Short' END AS waiting,
  is_canceled,
  COUNT(*),
  COUNT(*) * 100.0 / SUM(COUNT(*)) OVER (PARTITION BY waiting)
FROM test
GROUP BY waiting, is_canceled;
waiting is_canceled count(*) count() / sum(count()) over (partition by waiting)
Long 0 10 58.82353
Long 1 7 41.17647
Short 0 15 65.21739
Short 1 8 34.78261

Upvotes: 1

GMB
GMB

Reputation: 222482

I would use window functions to compute the average, then aggregation:

select waiting, is_cancelled, 
    count(*) / sum(count(*)) over(partition by waiting) as ratio
from (
    select b.*, 
        case when days_in_waiting_list > avg(days_in_waiting_list) over()
            then 'Long Wait'
            else 'Short wait'
        end as waiting
    from bookings b
) b
group by waiting, is_cancelled
order by waiting, is_cancelled

Upvotes: 1

yusuf hayırsever
yusuf hayırsever

Reputation: 701

WITH cte AS (
SELECT
CASE WHEN days_in_waiting_list > (SELECT AVG(days_in_waiting_list) FROM Bookings) 
THEN 'Long wait'
ELSE 'Short wait' 
END AS waiting, 
is_canceled,
COUNT(*) as subTotal, 
sum(count(*) over (partition by waiting ORDER BY is_canceled ASC) as totalSum,
FROM Bookings
GROUP BY waiting, is_canceled;
)
SELECT waiting,
is_canceled,
subTotal* (100.0)/totalSum as percentage
FROM cte
group by waiting,is_canceled

Upvotes: 1

Anggia Anggia
Anggia Anggia

Reputation: 11

you want the percentages to be calculated per category, thus grouping by waiting category is needed for perc_cancelled

count() * 100.0 / sum(count()) over(partition by waiting) AS perc_cancelled

Upvotes: 1

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