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Creating Single- and Multi-Column Primary Keys

using System; using System.Data;     class Program     {         static void Main(string[] args)         {             DataTable dt1 = new DataTable("Table-1");             DataColumn pkCol = dt1.Columns.Add("Id", typeof(int));             dt1.Columns.Add("Field1", typeof(string)).MaxLength = 50;             dt1.PrimaryKey = new DataColumn[] { pkCol };             DataTable dt2 = new DataTable("Table-2");             dt2.Columns.Add("Id", typeof(int));             dt2.Columns.Add("Field1", typeof(string)).MaxLength = 50;             UniqueConstraint uc = new UniqueConstraint("PrimaryKey-2", dt2.Columns["Id"], true);             dt2.Constraints.Add(uc);             DataTable dt3 = new DataTable("Table-3");             dt3.Columns.Add("Id1", typeof(int));             dt3.Columns.Add("Id2", typeof(int));             dt3.Columns.Add("Field1", typeof(string)).MaxLength = 50;             dt3.Constraints.Add("PrimaryKey-3",new DataColumn[] { dt3.Columns["Id1"], dt3.Columns["Id2"] },true);         }     }