Copied from https://www.simple-talk.com/sql/t-sql-programming/concatenating-row-values-in-transact-sql/
SELECT DISTINCT CategoryId ,ProductNames FROM Northwind.dbo.Products p1 CROSS APPLY ( SELECT ProductName + ‘,‘ FROM Northwind.dbo.Products p2 WHERE p2.CategoryId = p1.CategoryId ORDER BY ProductName FOR XML PATH(‘‘) ) D(ProductNames) ;
Concatenating Row Values in Transact-SQL
原文：http://www.cnblogs.com/hopecho/p/4242363.html