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34 lines
1.3 KiB
Plaintext
34 lines
1.3 KiB
Plaintext
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Expression indices
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------------------
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Function:
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Allow to index arbitrary expressions applied to the row values, hence allowing
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indexed access paths to be used for expression-based predicates.
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Author:
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Oleg Loa <loa@mail.ru>
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Dmitry Yemanov <yemanov@yandex.ru>
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Syntax rules:
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CREATE [UNIQUE] [{ASC[ENDING] | DESC[ENDING]}] INDEX <index_name> ON <table_name>
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COMPUTED [BY] ( <value_expression> )
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Scope:
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DSQL (DDL)
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Example(s):
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1. CREATE INDEX IDX1 ON T1 COMPUTED BY ( UPPER(COL1 COLLATE PXW_CYRL) );
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SELECT * FROM T1 WHERE UPPER(COL1 COLLATE PXW_CYRL) = '<capital cyrillic letters sequence>'
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-- PLAN (T1 INDEX (IDX1))
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2. CREATE INDEX IDX2 ON T2 COMPUTED BY ( EXTRACT(YEAR FROM COL2) || EXTRACT(MONTH FROM COL2) );
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SELECT * FROM T2 ORDER BY EXTRACT(YEAR FROM COL2) || EXTRACT(MONTH FROM COL2)
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-- PLAN (T2 ORDER IDX2)
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Note(s):
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1. An expression used in the index declaration must match a predicate expression precisely
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to allow the engine to choose an indexed access path. Otherwise, the given index won't be used
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for a retrieval/sorting.
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2. Expression indices have exactly the same features and limitations as usual indices, with the
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only exception that, by definition, they cannot be composite (multi-segment).
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