数据库表通常具有一个列或一组列，用于唯一标识表中的每一行。 此标识列或列组称为主键。
当您将单个DataColumn标识为PrimaryKeyDataTable时，表格会自动将列的AllowDBNull属性设置为false，并将Unique属性设置为true。 对于多列主键，仅属性 AllowDBNull 自动设置为 false。
DataTable的PrimaryKey属性的值是一个或多个DataColumn对象的数组，如以下示例所示。 第一个示例将单个列定义为主键。
workTable.PrimaryKey = New DataColumn() {workTable.Columns("CustID")}
' Or
Dim columns(1) As DataColumn
columns(0) = workTable.Columns("CustID")
workTable.PrimaryKey = columns
workTable.PrimaryKey = new DataColumn[] {workTable.Columns["CustID"]};
// Or
DataColumn[] columns = new DataColumn[1];
columns[0] = workTable.Columns["CustID"];
workTable.PrimaryKey = columns;
以下示例将两列定义为主键。
workTable.PrimaryKey = New DataColumn() {workTable.Columns("CustLName"), _
workTable.Columns("CustFName")}
' Or
Dim keyColumn(2) As DataColumn
keyColumn(0) = workTable.Columns("CustLName")
keyColumn(1) = workTable.Columns("CustFName")
workTable.PrimaryKey = keyColumn
workTable.PrimaryKey = new DataColumn[] {workTable.Columns["CustLName"],
workTable.Columns["CustFName"]};
// Or
DataColumn[] keyColumn = new DataColumn[2];
keyColumn[0] = workTable.Columns["CustLName"];
keyColumn[1] = workTable.Columns["CustFName"];
workTable.PrimaryKey = keyColumn;