DataTable dataTable = new DataTable();
 
DataColumn idColumn = new DataColumn( "id" );
idColumn.DataType = typeof( string );
 
// DataColumn has all the properties you would expect to find if you were creating a database field
 
idColumn.MaxLength = 10; // Default: -1
idColumn.Unique = true; // Default: false
idColumn.AllowDBNull = false; // Default: true;
 
// Add the column to the dataTable
dataTable.Columns.Add( idColumn );
// OR
dataTable.Columns.Add( "id", typeof( string ) );
DataColumn column = dataTable.Columns[ "id" ];
// ---------------------------
DataColumn salaray = new DataColumn( "salary" );
salary.DataType = typeof( Decimal );
salary.DefaultValue = 0.00m; // m = decimal literal
dataTable.Columns.Add( salary );
 
// Decimal - Fixed precision float - good for money
// Hex: int t = 0xc4;

DataRow row1 = dataTable.newRow();
row1["id"] = "x123";
row1["salary"] = 11043.00m;
dataTable.Rows.Add(row1);
// Alternatively
dataTable.Rows.Add("Z417", 32147.00m);
// Alternatively adding a row with an object array
dataTable.Rows.Add(new object[] { "P112", 7417.00m } );

row1.AcceptChanges(); // --> "commit"
row1.RejectChanges(); // --> "roll back"
label1.Text = "" + row1.RowState;

DataSet ds = new DataSet("db");
 
DataTable table1 = ds.Tables.Add("table1");
table1.Columns.Add("id", typeof(Guid)); // Guid: Global Unique Identifier
table1.Columns.Add("name", typeof(string));
table1.PrimaryKey = new DataColumn[] { table1.Columns["id"] };
 
DataTable table2 = ds.Tables.Add("table2");
table2.Columns.Add("id", typeof(Guid));
table2.Columns.Add("style", typeof(string));
table2.Columns.Add("foreign_key", typeof(Guid));
table2.PrimaryKey = new DataColumn[] { table2.Columns["id"] };
 
ds.Relations.Add("table1_table2_relation", table1.Columns["id"], table2.Columns["foreign_key"]);