Yaoxuan Wu created FLINK-41038:
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Summary: WHERE CAST(x AS DECIMAL(10, 2)) IS NULL returns NULL for
x when the cast overflows
Key: FLINK-41038
URL: https://issues.apache.org/jira/browse/FLINK-41038
Project: Flink
Issue Type: Bug
Components: Table SQL / Planner
Affects Versions: 2.3.0
Reporter: Yaoxuan Wu
{code:python}
from pyflink.table import EnvironmentSettings, TableEnvironment, DataTypes as D
t = TableEnvironment.create(EnvironmentSettings.in_batch_mode())
t.create_temporary_view('v', t.from_elements([(2147483647,)],
D.ROW([D.FIELD('x', D.INT())])))
t.execute_sql("SELECT x, CAST(x AS DECIMAL(10, 2)) FROM v").print()
# (2147483647, NULL) the cast overflows to NULL
t.execute_sql("SELECT x, x IS NULL FROM v WHERE CAST(x AS DECIMAL(10, 2)) IS
NULL").print()
# expected: (2147483647, FALSE)
# actual: (NULL, TRUE)
{code}
The cast overflows, so the filter correctly keeps the row, but the planner then
replaces {{x}} with a NULL literal ({{Calc(select=[null:INTEGER AS x],
where=[...])}}). It infers {{x IS NULL}} from the filter because Calcite's
{{RexUtil.canAssignFrom}} treats INT -> DECIMAL(10, 2) as a widening cast; it
compares precision and scale separately, although DECIMAL(10, 2) has only 8
integer digits. Streaming mode returns the same wrong value.
Reproduces on 2.0.1, 2.2.1, 2.3.0 and master.
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