T-SQL How to "Flatten" top 3 rows into a single row - sql

Question

I've searched for an answer to this question and found questions similar to my own, however I do not have a "ColumnHeader" column to denote which field the record should go into. Ex:
TSQL Pivot without aggregate function
trying to flatten rows into columns
Fetching Columns of a multiple rows in one row
My problem is thus - I have data in this format (selected as a top 3 result from a product recommendation query):
------------------------------
CustID | StyleNo | Brand | ID
------------------------------
1 | ABC | BrandA| 1
------------------------------
1 | DEF | BrandB| 2
------------------------------
1 | GHI | BrandC| 3
------------------------------
2 | JKL | BrandA| 4
------------------------------
2 | MNO | BrandB| 5
------------------------------
2 | PQR | BrandD| 6
------------------------------
That I'd like to make look like this:
-----------------------------------------------------------------
CustID | StyleNo1| StyleNo2| StyleNo3 | Brand1 | Brand2 | Brand3
-----------------------------------------------------------------
1 | ABC | DEF | GHI | BrandA | BrandB | BrandC
-----------------------------------------------------------------
2 | JKL | MNO | PQR | BrandA | BrandB | BrandD
-----------------------------------------------------------------
In order for my program to simply read the row of recommendations for each customer.
What I have attempted is a PIVOT - however I have nothing to really aggregate upon. I've also attempted the Min(Case...When...Then...End) as outlined in the second linked question, but as stated I don't have reference to a "Header" column.
The ID column is completely inconsequential for the time being, but it may help to solve this problem. It is NOT needed in the end result.
I am currently using SQLServer 2012

Answer 1

With the window function Row_Number() and a conditional aggregation
Select CustID
,StyleNo1 = max(case when RN=1 then StyleNo else null end)
,StyleNo2 = max(case when RN=2 then StyleNo else null end)
,StyleNo3 = max(case when RN=3 then StyleNo else null end)
,Brand1 = max(case when RN=1 then Brand else null end)
,Brand2 = max(case when RN=2 then Brand else null end)
,Brand3 = max(case when RN=3 then Brand else null end)
From (
Select *,RN = Row_Number() over (Partition By CustID Order by StyleNo,Brand)
From YourTable
) A
Where RN<=3
Group By CustID
Returns

Answer 2

What you are doing is called "pivoting" - for this you could use PIVOT. A better way IMHO is to use approach that Jeff Moden talks about in this article.
WITH idSort AS
(
SELECT *, rn = ROW_NUMBER() OVER (PARTITION BY CustID ORDER BY ID) FROM #yourTable
)
SELECT
CustID,
StyleNo1 = MAX(CASE rn WHEN 1 THEN StyleNo END),
StyleNo2 = MAX(CASE rn WHEN 2 THEN StyleNo END),
StyleNo3 = MAX(CASE rn WHEN 3 THEN StyleNo END),
Brand1 = MAX(CASE rn WHEN 1 THEN Brand END),
Brand2 = MAX(CASE rn WHEN 2 THEN Brand END),
Brand3 = MAX(CASE rn WHEN 3 THEN Brand END)
FROM idSort
GROUP BY CustID;

Answer 3

Other approach can be using CTE's and Cross Apply.
CREATE TABLE #UnFlattenedData
(
CustID TINYINT ,
StyleNo CHAR(3) ,
Brand CHAR(6) ,
ID TINYINT
);
INSERT INTO #UnFlattenedData
( CustID, StyleNo, Brand, ID )
VALUES ( 1, -- CustID - tinyint
'ABC', -- StyleNo - char(3)
'BrandA', -- Brand - char(6)
1 -- ID - tinyint
),
( 1, -- CustID - tinyint
'DEF', -- StyleNo - char(3)
'BrandB', -- Brand - char(6)
2 -- ID - tinyint
),
( 1, -- CustID - tinyint
'GHI', -- StyleNo - char(3)
'BrandC', -- Brand - char(6)
3 -- ID - tinyint
),
( 2, -- CustID - tinyint
'JKL', -- StyleNo - char(3)
'BrandA', -- Brand - char(6)
4 -- ID - tinyint
),
( 2, -- CustID - tinyint
'MNO', -- StyleNo - char(3)
'BrandB', -- Brand - char(6)
5 -- ID - tinyint
),
( 2, -- CustID - tinyint
'PQR', -- StyleNo - char(3)
'BrandD', -- Brand - char(6)
6 -- ID - tinyint
);
WITH cte
AS ( SELECT * ,
ROW_NUMBER() OVER ( PARTITION BY u1.CustID ORDER BY u1.ID ) AS R1
FROM #UnFlattenedData AS u1
),
u1
AS ( SELECT C1.CustID ,
U1.StyleNo ,
U1.Brand
FROM cte AS C1
INNER JOIN #UnFlattenedData AS U1 ON U1.CustID = C1.CustID
AND U1.ID = C1.ID
WHERE C1.R1 = 1
),
u2
AS ( SELECT C1.CustID ,
U1.StyleNo ,
U1.Brand
FROM cte AS C1
INNER JOIN #UnFlattenedData AS U1 ON U1.CustID = C1.CustID
AND U1.ID = C1.ID
WHERE C1.R1 = 2
),
u3
AS ( SELECT C1.CustID ,
U1.StyleNo ,
U1.Brand
FROM cte AS C1
INNER JOIN #UnFlattenedData AS U1 ON U1.CustID = C1.CustID
AND U1.ID = C1.ID
WHERE C1.R1 = 3
)
SELECT u1.CustID ,
u1.StyleNo AS StyleNo1 ,
u2.StyleNo AS StyleNo2 ,
u3.StyleNo AS StyleNo3 ,
u1.Brand AS Brand1 ,
u2.Brand AS Brand2 ,
u3.Brand AS Brand3
FROM u1
CROSS APPLY ( SELECT *
FROM u2
WHERE u2.CustID = u1.CustID
) AS u2
CROSS APPLY ( SELECT *
FROM u3
WHERE u3.CustID = u1.CustID
) AS u3;