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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