<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
<!-- This component and the accompanying materials are made available under the terms of the License 
"Eclipse Public License v1.0" which accompanies this distribution, 
and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
<!-- Initial Contributors:
    Nokia Corporation - initial contribution.
Contributors: 
-->
<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept xml:lang="en" id="GUID-7BE83158-B818-57E4-9A8C-43E5D2C84687"><title>DBMS columns, column sets, and keys overview</title><prolog><metadata><keywords/></metadata></prolog><conbody><section><title>Purpose</title> <p>Defines column, column set, and index key structures.</p> </section> <section><title>Description</title> <p>The API has three key concepts: column, column set, and index key. </p> <p><b>Column</b> </p> <p>A table in a database is defined by a set of columns. Each column has attributes such as a name, a type, and a maximum length (if text or binary). </p> <p>A column definition is encapsulated by <xref href="GUID-0130C7AA-B143-32A4-BB33-0D90CEDABAAE.dita"><apiname>TDbCol</apiname></xref>. </p> <p><b>Column set</b> </p> <p>A set of columns that describe a table are encapsulated in <xref href="GUID-9B02D75E-1EE0-349E-9900-BEC1CAF9DECE.dita"><apiname>CDbColSet</apiname></xref>. The set can be iterated over using <xref href="GUID-C76AA489-BFF5-3D6E-BB26-C84A3E7887ED.dita"><apiname>TDbColSetIter</apiname></xref>.</p> <p><b>Index key</b> </p> <p>An index key orders one or more table columns (keys). It has attributes such as being unique or primary, a comparison specification for text columns, and a list of columns which make up the key. </p> <p>The index key is encapsulated in <xref href="GUID-0CA88018-0265-3853-AC64-3B938DD0F60C.dita"><apiname>CDbKey</apiname></xref>. A column for the key is encapsulated in <xref href="GUID-DDB34DBF-4A96-3430-820A-97AB5585962D.dita"><apiname>TDbKeyCol</apiname></xref>.</p> </section> </conbody></concept>