Count Top 5 Elements spread over rows and columns - sql

Question

Using T-SQL for this table:
+-----+------+------+------+-----+
| No. | Col1 | Col2 | Col3 | Age |
+-----+------+------+------+-----+
| 1 | e | a | o | 5 |
| 2 | f | b | a | 34 |
| 3 | a | NULL | b | 22 |
| 4 | b | c | a | 55 |
| 5 | b | a | b | 19 |
+-----+------+------+------+-----+
I need to count the TOP 3 names (Ordered by TotalCount DESC) across all rows and columns, for 3 Age groups: 0-17, 18-49, 50-100. Also, how do I ignore the NULLS from my results?
If it's possible, how I can also UNION the results for all 3 age groups into one output table to get 9 results (TOP 3 x 3 Age groups)?
Output for only 1 Age Group: 18-49 would look like this:
+------+------------+
| Name | TotalCount |
+------+------------+
| b | 4 |
| a | 3 |
| f | 1 |
+------+------------+

Answer 1

You need to unpivot first your table and then exclude the NULLs. Then do a simple COUNT(*):
WITH CteUnpivot(Name, Age) AS(
SELECT x.*
FROM tbl t
CROSS APPLY ( VALUES
(col1, Age),
(col2, Age),
(col3, Age)
) x(Name, Age)
WHERE x.Name IS NOT NULL
)
SELECT TOP 3
Name, COUNT(*) AS TotalCount
FROM CteUnpivot
WHERE Age BETWEEN 18 AND 49
GROUP BY Name
ORDER BY COUNT(*) DESC
ONLINE DEMO
If you want to get the TOP 3 for each age group:
WITH CteUnpivot(Name, Age) AS(
SELECT x.*
FROM tbl t
CROSS APPLY ( VALUES
(col1, Age),
(col2, Age),
(col3, Age)
) x(Name, Age)
WHERE x.Name IS NOT NULL
),
CteRn AS (
SELECT
AgeGroup =
CASE
WHEN Age BETWEEN 0 AND 17 THEN '0-17'
WHEN Age BETWEEN 18 AND 49 THEN '18-49'
WHEN Age BETWEEN 50 AND 100 THEN '50-100'
END,
Name,
COUNT(*) AS TotalCount
FROM CteUnpivot
GROUP BY
CASE
WHEN Age BETWEEN 0 AND 17 THEN '0-17'
WHEN Age BETWEEN 18 AND 49 THEN '18-49'
WHEN Age BETWEEN 50 AND 100 THEN '50-100'
END,
Name
)
SELECT
AgeGroup, Name, TotalCount
FROM(
SELECT *,
rn = ROW_NUMBER() OVER(PARTITION BY AgeGroup, Name ORDER BY TotalCount DESC)
FROM CteRn
) t
WHERE rn <= 3;
ONLINE DEMO
The unpivot technique using CROSS APPLY and VALUES:
An Alternative (Better?) Method to UNPIVOT (SQL Spackle) by Dwain Camps

Answer 2

You can check below multiple-CTE SQL select statement
Row_Number() with Partition By clause is used ordering records within each group categorized by ages
/*
CREATE TABLE tblAges(
[No] Int,
Col1 VarChar(10),
Col2 VarChar(10),
Col3 VarChar(10),
Age SmallInt
)
INSERT INTO tblAges VALUES
(1, 'e', 'a', 'o', 5),
(2, 'f', 'b', 'a', 34),
(3, 'a', NULL, 'b', 22),
(4, 'b', 'c', 'a', 55),
(5, 'b', 'a', 'b', 19);
*/
;with cte as (
select
col1 as col, Age
from tblAges
union all
select
col2, Age
from tblAges
union all
select
col3, Age
from tblAges
), cte2 as (
select
col,
case
when age < 18 then '0-17'
when age < 50 then '18-49'
else '50-100'
end as grup
from cte
where col is not null
), cte3 as (
select
grup,
col,
count(grup) cnt
from cte2
group by
grup,
col
)
select * from (
select
grup, col, cnt, ROW_NUMBER() over (partition by grup order by cnt desc) cnt_grp
from cte3
) t
where cnt_grp <= 3
order by grup, cnt