Convert rows to columns with values based on ranking - sql

Question

I have a table of customers who have several kinds of "accounts", each with a different integer balance, such as
CUSTID AcctType Balance
12345 Checking 1000
12345 Savings 5000
12345 Investment 3000
98765 Savings 2000
98765 Checking 8000
98765 Investment 1000
98765 Retirement 2500
I do not know how many accounts a customer may have (it could be anywhere from 1 to 6). I have to create a result showing the Accounts and Balances as columns, in order from highest to lowest, like this:
CUSTID AcctType1 Balance1 AcctType2 Balance2 AcctType3 Balance3 AcctType4 Balance 4
12345 Savings 5000 Investment 3000 Checking 1000
98765 Checking 8000 Retirement 2500 Savings 2000 Investment 1000
Any ideas how to create this in SQL Server? (Ideally as a View)

Answer 1

You can unpivot the columns first into rows, then pivot the rows back into column with row number, something like this:
WITH CTE
AS
(
SELECT
CAST(CUSTID AS NVARCHAR(50)) AS CUSTID
,CAST(AcctType AS NVARCHAR(50)) AS AcctType
,CAST(Balance AS NVARCHAR(50)) AS Balance
,ROW_NUMBER() OVER(PARTITION BY [CUSTID] ORDER BY Balance DESC) AS RN
FROM Data
), unpivoted
AS
(
SELECT CUSTID, val, col + ' ' + CAST(RN AS NVARCHAR(50)) AS col
FROM CTE
UNPIVOT
(
val
FOR col IN(AcctType, Balance)
) AS u
)
SELECT *
FROM unpivoted AS u
PIVOT
(
MAX(val)
FOR col IN([AcctType 1], [Balance 1],
[AcctType 2], [Balance 2],
[AcctType 3], [Balance 3],
[AcctType 4], [Balance 4])
) AS p;
SQL Fiddle Demo
Update:
If you want to make this dynamic for any number of customers, you have to do it dynamically like this:
DECLARE #cols AS NVARCHAR(MAX);
DECLARE #query AS NVARCHAR(MAX);
WITH CTE
AS
(
SELECT
CAST(CUSTID AS NVARCHAR(50)) AS CUSTID
,CAST(AcctType AS NVARCHAR(50)) AS AcctType
,CAST(Balance AS NVARCHAR(50)) AS Balance
,ROW_NUMBER() OVER(PARTITION BY [CUSTID] ORDER BY Balance DESC) AS RN
FROM Data
), Data
AS
(
SELECT col, MAX(RN) AS RN
FROM
(
SELECT RN, col + CAST(RN AS NVARCHAR(50)) AS col
FROM CTE
UNPIVOT
(
val
FOR col IN(AcctType, Balance)
) AS u
) AS t
GROUP BY col
)
select #cols = STUFF((SELECT ',' +
QUOTENAME(col)
FROM Data
ORDER BY RN
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
, 1, 1, '');
SELECT #query = 'WITH CTE
AS
(
SELECT
CAST(CUSTID AS NVARCHAR(50)) AS CUSTID
,CAST(AcctType AS NVARCHAR(50)) AS AcctType
,CAST(Balance AS NVARCHAR(50)) AS Balance
,ROW_NUMBER() OVER(PARTITION BY [CUSTID] ORDER BY Balance DESC) AS RN
FROM Data
), unpivoted
AS
(
SELECT CUSTID, val, col + CAST(RN AS NVARCHAR(50)) AS col
FROM CTE
UNPIVOT
(
val
FOR col IN(AcctType, Balance)
) AS u
)
SELECT *
FROM unpivoted AS u
PIVOT
(
MAX(val)
FOR col IN('+ #cols + ')
) AS p;';
EXECUTE(#query);
Dynamic Demo

Answer 2

If it's a limited amount of columns(as you said 6 per CUSTID) then you can use conditional aggregation with ROW_NUMBER():
SELECT t.custID,
MAX(CASE WHEN t.rnk = 1 THEN t.accttype END) as accttype1,
MAX(CASE WHEN t.rnk = 1 THEN t.balance END) as balance1,
MAX(CASE WHEN t.rnk = 2 THEN t.accttype END) as accttype2,
MAX(CASE WHEN t.rnk = 2 THEN t.balance END) as balance2,
MAX(CASE WHEN t.rnk = 3 THEN t.accttype END) as accttype3,
MAX(CASE WHEN t.rnk = 3 THEN t.balance END) as balance3,
MAX(CASE WHEN t.rnk = 4 THEN t.accttype END) as accttype4,
MAX(CASE WHEN t.rnk = 4 THEN t.balance END) as balance4,
MAX(CASE WHEN t.rnk = 5 THEN t.accttype END) as accttype5,
MAX(CASE WHEN t.rnk = 5 THEN t.balance END) as balance5,
MAX(CASE WHEN t.rnk = 6 THEN t.accttype END) as accttype6,
MAX(CASE WHEN t.rnk = 6 THEN t.balance END) as balance6
FROM (SELECT s.*,
ROW_NUMBER() OVER(PARTITION BY s.custID ORDER BY s.balance DESC) as rnk
FROM YourTable s) t
GROUP BY t.custID