Question

I have a datatable from database on the basis of some query.

I want that datatable to have a primary key for an existing column.

How can I do this?

Answer 1

Assuming the name of the column in your data table you want to be the primary key is called pk_column, you could do this (assume dt is your DataTable):

dt.PrimaryKey = new DataColumn[] { dt.Columns["pk_column"] };

If your primary key is made up of multiple columns, you can add them to the array, like so:

dt.PrimaryKey = new DataColumn[] { dt.Columns["pk_column1"], dt.Columns["pk_column2"] };

So if you were making student_id your primary key, you could do this:

dt.PrimaryKey = new DataColumn[] { dt.Columns["student_id"] };