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<concept id="GUID-7BE83158-B818-57E4-9A8C-43E5D2C84687" xml:lang="en"><title>DBMS
columns, column sets, and keys overview</title><shortdesc>Defines column, column set, and index key structures.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<section id="GUID-3A16DD2F-0C12-4720-A52C-E7504850EB92"><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>