从动态字符串返回列名

I want to get the column from the dynamic string, In my table: MyTable2 I have many columns/fields, which are : MyVarCharColumnName1,MyVarCharColumnName2,MyVarCharColumnName3,MyVarCharColumnName4 These above fields are nvarchar(50), I wonder how I can get the value of them when join with another table as below example:I want to get the column from the dynamic strin