SELECT STUFF(( SELECT ',' + elmt.value('.', 'nvarchar(max)')
FROM ( SELECT (
/*YOUR QUERY HERE*/
SELECT DISTINCT mag_kod FROM tab
/*--------------------*/
/*--------------------*/
FOR XML AUTO ,ELEMENTS XSINIL ,TYPE ) ) AS A(t) CROSS APPLY t.nodes('/*/*')
AS B(elmt) FOR XML PATH('') ), 1, 1, '')
Działa to w MSSQL