Details
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Improvement
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Status: Resolved
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Major
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Resolution: Fixed
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None
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None
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None
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Docs Required, Release Notes Required
Description
Currently a full table scan will be executed in the case of disjunctive predicate even if predicate fields are indexed. For example:
SELECT * FROM emps WHERE name='A' OR surname='B'
This is caused by the nature of indexes: they can return cursor bounded by lower and upper bounds. We can cope with it by implementing a logical rule for rewriting OR query to a UNION ALL query:
SELECT * FROM emps WHERE name='A' UNION ALL SELECT * FROM emps WHERE surname='B' AND LNNVL(name='A')
where LNNVL() function has semantics
LNNVL(name='A') == name!='A' OR name=NULL.
It is used to avoid expensive deduplication. This name is taken from Oracle, we can think of more meaningful name, or find the analog in Calcite or H2.
See, for example, this blog post: https://blogs.oracle.com/optimizer/optimizer-transformations:-or-expansion for details.
Also it is needed to check this works for IN clause with small number of literals (AFAIK Calcite converts large IN clauses to a join with Values table where N > 20).
Attachments
Issue Links
- is part of
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IGNITE-12248 Apache Calcite based query execution engine
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- Open
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- links to
