How to merge column this specific way in SQL - sql

Question

My original table is this;
TableName= NewRetail
CustomerID 1 2 3 4 5 6 7.....30
1 30 31 Null Null Null Null Null
2 24 78 35 72 Null Null Null
I want to store this table in 'Retail'
CustomerId Itemset
1 30
1 31
2 24
2 78
2 35
2 72
There are no duplicates in any row in Original(Source) Table.
Thanks. I tried using Loops but couldn't make it work. Been stuck at it since three days.

Answer 1

You can use table valued constructor with Cross apply to unpivot the data
SELECT CustomerID,
Itemset
FROM Yourtable
CROSS apply (VALUES ([1]),([2]),([3]),([4]),([5]),([6]),([7]),...) cs (Itemset)
WHERE Itemset IS NOT NULL
Dynamic Version
DECLARE #itemset VARCHAR(max)='',
#sql NVARCHAR(max);
WITH cte
AS (SELECT TOP 30 Row_number()OVER(ORDER BY (SELECT NULL)) RN
FROM sys.columns)
SELECT #itemset += '(' + Quotename(RN) + '),'
FROM cte
SET #itemset = LEFT(#itemset, Len(#itemset) - 1)
SET #sql = 'SELECT CustomerID,
Itemset
FROM Yourtable
CROSS apply (VALUES ' + #itemset
+ ') cs (Itemset)
WHERE Itemset IS NOT NULL '
EXEC Sp_executesql #sql

Answer 2

You can do this using UNION ALL:
SELECT *
FROM (
SELECT CustomerId, [1] AS ItemSet FROM NewRetail UNION ALL
SELECT CustomerId, [2] FROM NewRetail UNION ALL
SELECT CustomerId, [3] FROM NewRetail UNION ALL
SELECT CustomerId, [4] FROM NewRetail UNION ALL
SELECT CustomerId, [5] FROM NewRetail UNION ALL
SELECT CustomerId, [6] FROM NewRetail UNION ALL
SELECT CustomerId, [7] FROM NewRetail UNION ALL
...
SELECT CustomerId, [30] FROM NewRetail
)t
WHERE ItemSet IS NOT NULL
ORDER BY CustomerId
Using dynamic SQL:
;WITH Tally(N) AS(
SELECT TOP 30 ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) FROM sys.columns
)
SELECT #sql = #sql +
CASE
WHEN #sql = '' THEN 'SELECT CustomerId, [' + CONVERT(VARCHAR(2), N) + '] AS ItemSet FROM NewRetail'
ELSE ' UNION ALL' + CHAR(10) +' SELECT CustomerId, [' + CONVERT(VARCHAR(2), N) + '] FROM NewRetail'
END
FROM Tally
SELECT #sql =
'SELECT *
FROM (
' + #sql + CHAR(10) +
')t
WHERE ItemSet IS NOT NULL
ORDER BY CustomerId'
PRINT #sql
EXEC (#sql)

Answer 3

It is a simple UNPIVOT operation. NULLs automatically eliminated from result:
declare #t table(custid int, [1] int, [2] int, [3] int)
insert into #t values
(1, 10, 30, null),
(2, 30, 40, 50)
select custid, c from #t
unpivot(c for p in([1], [2], [3])) p
Fiddle http://sqlfiddle.com/#!6/9eecb/1733