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<concept xml:lang="en" id="GUID-79B699F5-5EDE-5561-A385-19ED02248398"><title>Indexes</title><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>