How can create dynamic query from datatable C#

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C#

LINQ

I want to reformat the data without going back to the database and in a dynamic way So that the user can specify what columns he wants to collect

What I have tried:

how I can Write an sql string and execute it like EXECUTE IMMEDIAT in Oracle 
<pre lang="SQL">EXECUTE IMMEDIATE 'select field1 + field2 as f12 , field3 from table '

Inside C# Linq want to do a lock like combining two or more fields (multiply - merge...) ToTable It only allows me to specify the names of existing fields

FillDataSorce(params classP[] P)
{
 BSo.DataSource = from d in dt.AsEnumerable()
                    select new 
                    {
                       P.Select(p => p) //col3col2 = d["col1"] + d["col2"] Dynamic field example
                       
                    };
}