Translating MySQL statement to MS SQL (no GROUP_CONCAT) - sql

Question

I'm trying to translate the query from my question in SQL multiple rows as columns (optimizing). It is in MySQL but I need it to also run on a MS SQL Server.
One problem is that there is no GROUP_CONCAT in MS SQL, but there seems to be ways to simulate this however (Simulating group_concat MySQL function in Microsoft SQL Server 2005?).
Also, I can't find a way to to store the first SELECT statement into the #sql variable the same way which troubles me as I don't know how to then reference colkey as I currently do.
The MySQL statement:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT('MAX(CASE
WHEN ckm.colkey = ', colkey, ' THEN
(ccdr.value)
END) AS ', CONCAT('`ExtraColumn_', colkey, '`'))
) INTO #sql
FROM test_customkeymapping;
SET #sql = CONCAT('SELECT c.Name, ', #sql, '
FROM customers c
LEFT JOIN customercustomdatarels ccdr
ON c.Id = ccdr.customer
LEFT JOIN customdatas cd
ON cd.Id = ccdr.customdata
LEFT JOIN test_customkeymapping ckm
ON cd.key = ckm.customkey
GROUP BY c.Id');
PREPARE stmt FROM #sql;
EXECUTE stmt;

Answer 1

In SQL Server you need to make the following changes
Explicitly declare your variable with a type
Use + to concatenate strings instead of CONCAT (Unless you are using SQL Server 2012 or later)
Use brackets ([]) for object names/aliases instead of backticks (``) - QUOTENAME will do this for you
Use XML extensions to concatenate rows
Include c.Name in the group by as it is contained in the select
Use SP_EXECUTESQL to actually execute your query
So your query becomes something like:
DECLARE #SQL NVARCHAR(MAX);
SET #SQL = 'SELECT c.Name' + ( SELECT DISTINCT
', MAX(CASE WHEN ckm.colkey = '
+ QUOTENAME(colKey AS VARCHAR(10))
+ ' THEN (ccdr.value) END) AS '
+ QUOTENAME('ExtraColumn_' + CAST(colKey AS VARCHAR(10))
FROM test_customkeymapping
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)') +
'FROM customers c
LEFT JOIN customercustomdatarels ccdr
ON c.Id = ccdr.customer
LEFT JOIN customdatas cd
ON cd.Id = ccdr.customdata
LEFT JOIN test_customkeymapping ckm
ON cd.[key] = ckm.customkey
GROUP BY c.ID, c.Name';
EXECUTE SP_EXECUTESQL #SQL;