| title | ms.custom | ms.date | ms.prod | ms.reviewer | ms.suite | ms.technology | ms.tgt_pltfrm | ms.topic | ms.assetid | caps.latest.revision | author | ms.author | manager | |
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Defining Primary Keys |
03/30/2017 |
.net-framework |
|
article |
2ea85959-e763-4669-8bd9-46a9dab894bd |
4 |
JennieHubbard |
jhubbard |
jhubbard |
Defining Primary Keys
A database table commonly has a column or group of columns that uniquely identifies each row in the table. This identifying column or group of columns is called the primary key.
When you identify a single xref:System.Data.DataColumn as the xref:System.Data.DataTable.PrimaryKey%2A for a xref:System.Data.DataTable, the table automatically sets the xref:System.Data.DataColumn.AllowDBNull%2A property of the column to false and the xref:System.Data.DataColumn.Unique%2A property to true. For multiple-column primary keys, only the AllowDBNull property is automatically set to false.
The PrimaryKey property of a xref:System.Data.DataTable receives as its value an array of one or more DataColumn objects, as shown in the following examples. The first example defines a single column as the primary key.
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; The following example defines two columns as a primary key.
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; See Also
xref:System.Data.DataTable
DataTable Schema Definition
DataTables
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