How to declare the columns dynamically in a Select query using PIVOT - sql

Question

I am writing a query to get the address for PersonID. Following query is working for me but it only returns with two Addresses. I want to handle the 'n' number of address with a single query. Is there any way to do this?
Many thanks
SELECT
PersonID, PersonName
[Address1], [Address2]
FROM
(
SELECT
P.PersonID,
P.PersonName,
(ROW_NUMBER() OVER(PARTITION BY P.PersonID ORDER BY A.AddressID)) RowID
FROM tblPerson
INNER JOIN tblAddress AS A ON A.PersonID = P.PersonID
) AS AddressTable
PIVOT
(
MAX(AddressID)
FOR RowID IN ([Address1], [Address2])
) AS PivotTable;

Answer 1

Assuming the following tables and sample data:
USE tempdb;
GO
CREATE TABLE dbo.tblPerson(PersonID INT, PersonName VARCHAR(255));
INSERT dbo.tblPerson SELECT 1, 'Bob'
UNION ALL SELECT 2, 'Charlie'
UNION ALL SELECT 3, 'Frank'
UNION ALL SELECT 4, 'Amore';
CREATE TABLE dbo.tblAddress(AddressID INT, PersonID INT, [Address] VARCHAR(255));
INSERT dbo.tblAddress SELECT 1,1,'255 1st Street'
UNION ALL SELECT 2,2,'99 Elm Street'
UNION ALL SELECT 3,2,'67 Poplar Street'
UNION ALL SELECT 4,2,'222 Oak Ave.'
UNION ALL SELECT 5,1,'36 Main Street, Suite 22'
UNION ALL SELECT 6,4,'77 Sicamore Ct.';
The following query gets the results you want, and shows how it handles 0, 1 or n addresses. In this case the highest number is 3 but you can play with more addresses if you like by adjusting the sample data slightly.
DECLARE #col NVARCHAR(MAX) = N'',
#sel NVARCHAR(MAX) = N'',
#from NVARCHAR(MAX) = N'',
#query NVARCHAR(MAX) = N'';
;WITH m(c) AS
(
SELECT TOP 1 c = COUNT(*)
FROM dbo.tblAddress
GROUP BY PersonID
ORDER BY c DESC
)
SELECT #col = #col + ',[Address' + RTRIM(n.n) + ']',
#sel = #sel + ',' + CHAR(13) + CHAR(10) + '[Address' + RTRIM(n.n) + '] = x'
+ RTRIM(n.n) + '.Address',
#from = #from + CHAR(13) + CHAR(10) + ' LEFT OUTER JOIN xMaster AS x'
+ RTRIM(n.n) + ' ON x' + RTRIM(n.n) + '.PersonID = p.PersonID AND x'
+ RTRIM(n.n) + '.rn = ' + RTRIM(n.n)
FROM m CROSS JOIN (SELECT n = ROW_NUMBER() OVER (ORDER BY [object_id])
FROM sys.all_columns) AS n WHERE n.n <= m.c;
SET #query = N';WITH xMaster AS
(
SELECT PersonID, Address,
rn = ROW_NUMBER() OVER (PARTITION BY PersonID ORDER BY Address)
FROM dbo.tblAddress
)
SELECT PersonID, PersonName' + #col
+ ' FROM
(
SELECT p.PersonID, p.PersonName, ' + STUFF(#sel, 1, 1, '')
+ CHAR(13) + CHAR(10) + ' FROM dbo.tblPerson AS p ' + #from + '
) AS Addresses;';
PRINT #query;
--EXEC sp_executesql #query;
If you print the SQL you will see this result:
;WITH xMaster AS
(
SELECT PersonID, Address,
rn = ROW_NUMBER() OVER (PARTITION BY PersonID ORDER BY Address)
FROM dbo.tblAddress
)
SELECT PersonID, PersonName,[Address1],[Address2],[Address3] FROM
(
SELECT p.PersonID, p.PersonName,
[Address1] = x1.Address,
[Address2] = x2.Address,
[Address3] = x3.Address
FROM dbo.tblPerson AS p
LEFT OUTER JOIN xMaster AS x1 ON x1.PersonID = p.PersonID AND x1.rn = 1
LEFT OUTER JOIN xMaster AS x2 ON x2.PersonID = p.PersonID AND x2.rn = 2
LEFT OUTER JOIN xMaster AS x3 ON x3.PersonID = p.PersonID AND x3.rn = 3
) AS Addresses;
If you execute it, you will see this:
I know the query to get here is an ugly mess, but your requirement dictates it. It would be easier to return a comma-separated list as I suggested in my comment, or to have the presentation tier deal with the pivoting.