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7 Nokia Corporation - initial contribution. |
7 Nokia Corporation - initial contribution. |
8 Contributors: |
8 Contributors: |
9 --> |
9 --> |
10 <!DOCTYPE concept |
10 <!DOCTYPE concept |
11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
12 <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> |
12 <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 |
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13 when using <codeph>LongText</codeph> data types.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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14 <p>Indexes in the store database are B+tree structures with a fixed size key. |
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15 This means that text keys may easily generate large indexes, and a maximum |
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16 length text column cannot be indexed. </p> |
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17 <p>Keys in DBMS may be truncated by specifying the length of a text column |
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18 to be used in the index key. Such a key column must always be the last one |
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19 in the key, to ensure that the index provides a true ordering. If a text key |
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20 column does not supply a truncation length, the full length of the table column |
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21 is used.</p> |
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22 <p>Apart from <codeph>Binary</codeph> and <codeph>LongBinary</codeph> columns, |
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23 all types can be used in an index key including <codeph>LongText8</codeph> and <codeph>LongText16</codeph>, |
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24 although these must supply a truncation length (as they have no maximum length) |
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25 and must therefore be the last key columns in the key.</p> |
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26 </conbody></concept> |