How to count the number of occurrence in 4 columns - sql

Question

I have a T-SQL query to do in the most efficient way as possible.
Here is an example of my table:
A
B
C
D
E
1
x, y
z
NULL
NULL
2
x
NULL
NULL
y
3
y
z
NULL
NULL
4
a
NULL
b
x
Now, I need to do a query to classify my best matching records. Let's say that I need to take the top 3 records that match the more of the values 'x' & 'y' (it could be more than 2 values) into the columns B, C, D, E
A
NumberOfMatches
Comment
1
2
Because Column B contains x, y
2
2
Because Column B contains x & Column E contains y
3
1
Because Column B contains y
4
1
Because Column E contains x
Could you help me to find a good way to do this query?

Answer 1

I would highly recommend that you change how your data is stored, storing delimited strings to record multiple values is a recipe for disaster. If you have a one to many relationship use a child table with a foreign key to the main table. There is very rarely a reason to store delimited data like this, and when you have to query it and manipulate it you realise why it is not advised.
Assuming that each of your columns are the same and can hold many values, you'll need to split all of them, which you can do using this:
SELECT t.A, upvt.Col, Value = TRIM(ss.value)
FROM #T AS t
CROSS APPLY (VALUES ('B', t.B), ('C', t.C), ('D', t.D), ('E', t.E)) upvt (Col, Value)
CROSS APPLY STRING_SPLIT(upvt.Value, ',') AS ss;
Which gives:
A
Col
Value
1
B
x
1
B
y
1
C
z
2
B
x
2
E
y
3
B
y
3
C
z
4
B
a
4
D
b
4
E
x
With this normalised data, you can then just do a simple WHERE Value IN ('x', 'y') along with GROUP BY and COUNT(*):
IF OBJECT_ID(N'tempdb..#T ', 'U') IS NOT NULL
DROP TABLE #T ;
CREATE TABLE #T (A INT, B VARCHAR(4), C VARCHAR(4), D VARCHAR(4), E VARCHAR(4));
INSERT #T(A, B, C, D, E)
VALUES
(1, 'x, y', 'z', NULL, NULL),
(2, 'x', NULL, NULL, 'y'),
(3, 'y', 'z', NULL, NULL),
(4, 'a', NULL, 'b', 'x');
SELECT t.A, NumberOfMatches = COUNT(*)
FROM #T AS t
CROSS APPLY (VALUES (t.B), (t.C), (t.D), (t.E)) upvt (Value)
CROSS APPLY STRING_SPLIT(upvt.Value, ',') AS ss
WHERE TRIM(ss.value) IN ('x', 'y')
GROUP BY t.A
ORDER BY COUNT(*) DESC, t.A;

Answer 2

If you can't normalize the model you can use this query to get your expected result:
select a, count(*) numberOfMatches,
concat('Because column ', string_agg(columnName, ', ')) AS comment
from (
select a, columnName, trim(value) targetValue from (
select a, columnName, value result
from tbl unpivot (value for columnName in ([B], [C], [D], [E])) up
) t
outer apply string_split(result,',')
) r
where targetValue in ('x','y')
group by a
-- Result
/*
a numberOfMatches comment
1 2 Because column B, B
2 2 Because column B, E
3 1 Because column B
4 1 Because column E
*/
Update
You can use this custom function in order to implement string_split in SQL Server prior versions.
IF OBJECT_ID('[dbo].[STRING_SPLIT]','IF') IS NULL BEGIN
EXEC ('CREATE FUNCTION [dbo].[STRING_SPLIT] () RETURNS TABLE AS RETURN SELECT 1 X')
END
GO
ALTER FUNCTION [dbo].[STRING_SPLIT]
(
#string nvarchar(MAX),
#separator nvarchar(MAX)
)
RETURNS TABLE WITH SCHEMABINDING
AS RETURN
WITH X(N) AS (SELECT 'Table1' FROM (VALUES (0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) T(C)),
Y(N) AS (SELECT 'Table2' FROM X A1, X A2, X A3, X A4, X A5, X A6, X A7, X A8) , -- Up to 16^8 = 4 billion
T(N) AS (SELECT TOP(ISNULL(LEN(#string),0)) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) -1 N FROM Y),
Delim(Pos) AS (SELECT t.N FROM T WHERE (SUBSTRING(#string, t.N, LEN(#separator+'x')-1) LIKE #separator OR t.N = 0)),
Separated(value) AS (SELECT SUBSTRING(#string, d.Pos + LEN(#separator+'x')-1, LEAD(d.Pos,1,2147483647) OVER (ORDER BY (SELECT NULL)) - d.Pos - LEN(#separator))
FROM Delim d
WHERE #string IS NOT NULL)
SELECT s.value
FROM Separated s
WHERE s.value <> #separator
GO
Update 2
Just 1 if the field has x,y at the same time:
select a, count(distinct columnName) numberOfMatches,
concat('Because column ', string_agg(columnName, ', ')) AS comment
from (
select a, columnName, trim(value) targetValue from (
select a, columnName, value result
from tbl unpivot (value for columnName in ([B], [C], [D], [E])) up
) t
outer apply string_split(result,',')
) r
where targetValue in ('x','y')
group by a
/* another alternative */
select a, count(*) numberOfMatches,
concat('Because column ', string_agg(columnName, ', ')) AS comment
from (
select a, columnName, value targetValue
from tbl unpivot (value for columnName in ([B], [C], [D], [E])) up
) t
where targetValue like '%x%' or targetValue like '%y%'
group by a
-- Result
/*
a numberOfMatches comment
1 1 Because column B
2 2 Because column B, E
3 1 Because column B
4 1 Because column E
*/