Ilya Soin created FLINK-36561:
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Summary: ResultSet.wasNull() does not reflect null values in Flink
JDBC Driver
Key: FLINK-36561
URL: https://issues.apache.org/jira/browse/FLINK-36561
Project: Flink
Issue Type: Bug
Components: Table SQL / JDBC
Affects Versions: 1.19.1, 1.20.0, 1.18.1
Reporter: Ilya Soin
As per JDBC
[standard|https://docs.oracle.com/en/java/javase/17/docs/api/java.sql/java/sql/ResultSet.html#wasNull()],
{{ResultSet.wasNull()}}
{quote}Reports whether the last column read had a value of SQL NULL. Note that
you must first call one of the getter methods on a column to try to read its
value and then call the method wasNull to see if the value read was SQL NULL.
{quote}
However, Flink JDBC driver currently does not update the {{wasNull}} flag
within the {{FlinkResultSet.get*()}} methods. Instead, it only sets this flag
during [iteration over
rows|https://github.com/apache/flink/blob/release-2.0-preview1-rc1/flink-table/flink-sql-jdbc-driver/src/main/java/org/apache/flink/table/jdbc/FlinkResultSet.java#L106]
fetched from the gateway endpoint. This behavior leads to {{wasNull}}
returning true only if the entire row is null, not when individual column
values are null. Consequently, reading a null value using
{{FlinkResultSet.get*()}} incorrectly results in {{wasNull()}} returning false,
which is not compliant with the JDBC specification.
h4. Proposed solution
Check if the underlying value accessed with {{FlinkResultSet.get*()}} method is
null, and update wasNull accordingly.
h4. For discussion
Can we skip null rows in FlinkResultSet.next()?
h4. Steps to reproduce:
Add
{code:java}
assertTrue(resultSet.wasNull());
{code}
after any call to resultSet.get*() in
[testStringResultSetNullData()|https://github.com/apache/flink/blob/release-2.0-preview1-rc1/flink-table/flink-sql-jdbc-driver/src/test/java/org/apache/flink/table/jdbc/FlinkResultSetTest.java#L115].
Run the test and see the failed check.
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