sepuri sai krishna created FLINK-40338:
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Summary: ELT() throws ClassCastException when the index argument
is not INT
Key: FLINK-40338
URL: https://issues.apache.org/jira/browse/FLINK-40338
Project: Flink
Issue Type: Bug
Components: Table SQL / Runtime
Affects Versions: 2.3.0, 2.2.0, 2.1.0, 2.0.0
Reporter: sepuri sai krishna
{{ELT}} accepts any {{INTEGER_NUMERIC}} index. {{IndexArgumentTypeStrategy}}
returns the argument's own data type unchanged (no implicit cast to {{INT}}),
and the documentation lists the supported signatures as:
{noformat}
index <TINYINT | SMALLINT | INTEGER | BIGINT>, expr <CHAR | VARCHAR>, exprs
<CHAR | VARCHAR>
index <TINYINT | SMALLINT | INTEGER | BIGINT>, expr <BINARY | VARBINARY>, exprs
<BINARY | VARBINARY>
{noformat}
But {{EltFunction#eval}} indexes the varargs array with {{exprs[(int) index -
1]}}, where {{index}} is declared as {{java.lang.Number}}. Per JLS 5.5, casting
a {{Number}} reference to {{int}} compiles to a narrowing reference conversion
to {{Integer}} followed by unboxing, i.e. {{((Integer) index).intValue()}}. The
call therefore succeeds only when the boxed value is exactly an {{Integer}}; a
{{Byte}}, {{Short}} or {{Long}} fails the {{checkcast}}.
h3. Reproducer
{code:sql}
SELECT ELT(CAST(2 AS BIGINT), 'scala', 'java');
{code}
{noformat}
java.lang.ClassCastException: class java.lang.Long cannot be cast to class
java.lang.Integer
{noformat}
Same for {{CAST(2 AS TINYINT)}} and {{CAST(2 AS SMALLINT)}}.
h3. Why this was not caught
The out-of-range guard above the cast uses {{index.longValue()}}, so
out-of-range indices of any type still return {{NULL}} correctly. The exception
only fires on the success path, when {{1 <= index <= number of expressions}}.
That is why the existing test {{ELT(9223372036854775807, 'ab', 'b')}} passes --
it returns {{NULL}} before ever reaching the cast. Every other existing test
uses an {{INT}} literal.
h3. Fix
Narrow the already-unboxed {{long idx}} rather than casting the {{Number}}
reference.
Present since FLINK-35987 introduced ELT; confirmed absent from release-1.20
and present from release-2.0.
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