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<concept id="GUID-79B699F5-5EDE-5561-A385-19ED02248398" xml:lang="en"><title>Indexes</title><shortdesc>Most datatypes can be used in indexes, but there are restrictions

when using <codeph>LongText</codeph> data types.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Indexes in the store database are B+tree structures with a fixed size key.

This means that text keys may easily generate large indexes, and a maximum

length text column cannot be indexed. </p>

<p>Keys in DBMS may be truncated by specifying the length of a text column

to be used in the index key. Such a key column must always be the last one

in the key, to ensure that the index provides a true ordering. If a text key

column does not supply a truncation length, the full length of the table column

is used.</p>

<p>Apart from <codeph>Binary</codeph> and <codeph>LongBinary</codeph> columns,

all types can be used in an index key including <codeph>LongText8</codeph> and <codeph>LongText16</codeph>,

although these must supply a truncation length (as they have no maximum length)

and must therefore be the last key columns in the key.</p>

</conbody></concept>