Yuval Itzchakov created FLINK-14533:
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Summary: PushFilterIntoTableSourceScanRule misses predicate pushdowns
Key: FLINK-14533
URL:
https://issues.apache.org/jira/browse/FLINK-14533 Project: Flink
Issue Type: Bug
Components: Table SQL / Planner
Affects Versions: 1.9.1, 1.9.0, 1.8.2, 1.8.1
Reporter: Yuval Itzchakov
When Flink attempts to perform predicate pushdown via `PushFilterIntoTableSourceScanRule`, it first checks the RexNodes to see if they can actually be pushed down to the source. It does that via `RexNodeToExpressionConverter.visitCall`, which traverses the nodes and eventually checks to see if it's a condition it knows:
{code:scala}
call.getOperator match {
case SqlStdOperatorTable.OR => Option(operands.reduceLeft { (l, r) => Or(l.asInstanceOf[PlannerExpression], r.asInstanceOf[PlannerExpression]) })
case SqlStdOperatorTable.AND => Option(operands.reduceLeft { (l, r) => And(l.asInstanceOf[PlannerExpression], r.asInstanceOf[PlannerExpression]) })
case function: SqlFunction => lookupFunction(replace(function.getName), operands)
case postfix: SqlPostfixOperator => lookupFunction(replace(postfix.getName), operands)
case operator@_ => lookupFunction(replace(s"${operator.getKind}"), operands)
}
{code}
If we take as an example the following query:
{code:sql}
SELECT a, b, c
FROM d
WHERE LOWER(a) LIKE '%%foo%%' AND LOWER(b) LIKE '%%python%%'
{code}
When we hit the above pattern match, we fall to the case matching `SqlFunction`, as `LOWER` is of that type. Inside `lookupFunction`, we have a call to `functionCatalog.lookupFunction(name)` which looks up the given function in the function catalog. Eventually, we reach a static class called `BuiltInFunctionDefinitions`, which defines all of Flink's built in functions. When we iterate the list of built in functions as follows:
{code:java}
foundDefinition = BuiltInFunctionDefinitions.getDefinitions()
.stream()
.filter(f -> functionName.equals(normalizeName(f.getName())))
.findFirst()
.map(Function.identity());
{code}
This doesn't yield a result, because `LOWER`, inside `BuiltInFunctionDefinitions`, is defined as follows:
{code:java}
public static final BuiltInFunctionDefinition LOWER =
new BuiltInFunctionDefinition.Builder()
.name("lowerCase")
.kind(SCALAR)
.outputTypeStrategy(TypeStrategies.MISSING)
.build();
{code}
And since we're using String to do the lookups, this fails to match, hence returning `null` and causing the entire pushdown to fail.
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