[jira] [Created] (IGNITE-13021) Calcite integration. Avoid full scans for disjunctive queries.

["Roman Kondakov (Jira)" <ji...@apache.org>]

Roman Kondakov created IGNITE-13021:
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             Summary: Calcite integration. Avoid full scans for disjunctive queries.
                 Key: IGNITE-13021
                 URL: https://issues.apache.org/jira/browse/IGNITE-13021
             Project: Ignite
          Issue Type: Improvement
          Components: sql
            Reporter: Roman Kondakov


Currently a full table scan will be executed in the case of disjunctive predicate even if predicate fields are indexed. For example:

{code:java}
SELECT * FROM emps WHERE name='A' OR surname='B'
{code}

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:

{code:java}
SELECT * FROM emps WHERE name='A' 
UNION ALL
SELECT * FROM emps WHERE surname='B'  AND LNNVL(name='A')
{code}
where {{LNNVL()}} function has semantics 
{code:java}
LNNVL(name='A') == name!='A' OR name=NULL.
{code}
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.



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