Ruben Q L created CALCITE-7140:
----------------------------------
Summary: Improve constant reduction of expressions containing
SqlRowOperator
Key: CALCITE-7140
URL: https://issues.apache.org/jira/browse/CALCITE-7140
Project: Calcite
Issue Type: Improvement
Components: core
Reporter: Ruben Q L
Currently, if we have a query like this (e.g. to be included in
RelOptRulesTest):
{code:java}
@Test void testCardinality() {
final String sql = "SELECT CARDINALITY(ARRAY[1, 2])";
sql(sql).withRule(CoreRules.PROJECT_REDUCE_EXPRESSIONS).check();
}
{code}
It is correctly reduced as "2" by the ReduceExpressionsRule:
{code:xml}
<TestCase name="testCardinality">
<Resource name="sql">
<![CDATA[SELECT CARDINALITY(ARRAY[1, 2])]]>
</Resource>
<Resource name="planBefore">
<![CDATA[
LogicalProject(EXPR$0=[CARDINALITY(ARRAY(1, 2))])
LogicalValues(tuples=[[{ 0 }]])
]]>
</Resource>
<Resource name="planAfter">
<![CDATA[
LogicalProject(EXPR$0=[2])
LogicalValues(tuples=[[{ 0 }]])
]]>
</Resource>
</TestCase>
{code}
However, a similar query containing constant structs:
{code:java}
@Test void testCardinalityWithRow() {
final String sql = "SELECT CARDINALITY(ARRAY[ROW(1,'a'), ROW(2,'b')])";
sql(sql).withRule(CoreRules.PROJECT_REDUCE_EXPRESSIONS).check();
}
{code}
Is not reduced and remains unchanged:
{code:xml}
<TestCase name="testCardinalityWithRow">
<Resource name="sql">
<![CDATA[SELECT CARDINALITY(ARRAY[ROW(1,'a'), ROW(2,'b')])]]>
</Resource>
<Resource name="planBefore">
<![CDATA[
LogicalProject(EXPR$0=[CARDINALITY(ARRAY(ROW(1, 'a'), ROW(2, 'b')))])
LogicalValues(tuples=[[{ 0 }]])
]]>
</Resource>
<Resource name="planAfter">
<![CDATA[
LogicalProject(EXPR$0=[2])
LogicalValues(tuples=[[{ 0 }]])
]]>
</Resource>
</TestCase>
=>
org.opentest4j.AssertionFailedError: planAfter ==> expected: <
LogicalProject(EXPR$0=[2])
LogicalValues(tuples=[[{ 0 }]])
> but was: <
LogicalProject(EXPR$0=[CARDINALITY(ARRAY(ROW(1, 'a'), ROW(2, 'b')))])
LogicalValues(tuples=[[{ 0 }]])
{code}
The reason is that [ReduceExpressionsRule#ReducibleExprLocator a RexCall with
SqlRowOperator is considered
non-constant|https://github.com/apache/calcite/blob/3ceb364c158e80c59a89137c85637ad53f4c0fab/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L1150],
since the "Row operator itself can't be reduced to a literal"; however, in
cases like this one, a RexCall (e.g. cardinality) containing a SqlRowOperator
can be potentially reduced.
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