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https://issues.apache.org/jira/browse/CALCITE-7062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17983740#comment-17983740
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Julian Hyde commented on CALCITE-7062:
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Is there a test case that produces an exception? Try adding 1 to the column.
> Row type of UNION may ignore a column's nullability
> ---------------------------------------------------
>
> Key: CALCITE-7062
> URL: https://issues.apache.org/jira/browse/CALCITE-7062
> Project: Calcite
> Issue Type: Bug
> Affects Versions: 1.39.0, 1.40.0
> Reporter: Vladimir Steshin
> Priority: Minor
>
> I'm not sure this is a problem. Is that ok? I found it by one of type casting
> tests.
> Consider:
> {code:java}
> package org.apache.calcite.test;
> class ServerTest {
> @Test void testNullableCoercionInUnion() throws Exception {
> try (Connection c = connect(); Statement s = c.createStatement()) {
> s.execute("create table t1 (i smallint not null)");
> s.execute("create table t2 (i bigint)");
> s.executeUpdate("insert into t1 values (1)");
> s.executeUpdate("insert into t2 values (10), (null)");
> try (ResultSet r = s.executeQuery("select i from t1 union all select i
> from t2")) {
> assertTrue(r.next());
> assertThat(r.getLong("i"), is(1L));
> assertTrue(r.next());
> assertThat(r.getLong("i"), is(10L));
> assertTrue(r.next());
> // The result has a null value. It is ok.
> assertNull(r.getObject("i"));
> }
> // The plan.
> try (ResultSet r = s.executeQuery("explain plan for select i from t1
> union all select i from t2")) {
> assertTrue(r.next());
> String plan = r.getString(1);
> // Fails here. It actually casts to a BIGINT NOT NULL whereas the
> actual resuls contain a NULL.
> assertTrue(plan.contains("[CAST($t0):BIGINT]"));
> }
> }
> }
> } {code}
> The least restrictive type is _nullable BIGINT._ Looks ok. However,
> _StandardConvertletTable#convertCast(...)_ produces a _CAST_ to a {_}NOT
> NULLABLE{_}.
> Regarding my research, the nullability is lost somewhere around
> {code:java}
> class AbstractTypeCoercion
> RelDataType syncAttributes(
> RelDataType fromType,
> RelDataType toType) {
> RelDataType syncedType = toType;
> if (fromType != null) {
> syncedType = factory.createTypeWithNullability(syncedType,
> fromType.isNullable());
> ...
> }{code}
> It doesn't take in account {_}toType.isNullable(){_}.
> And also in
> {code:java}
> class SqlCastFunction
> private static RelDataType
> createTypeWithNullabilityFromExpr(RelDataTypeFactory typeFactory,
> RelDataType expressionType, RelDataType targetType, boolean safe) {
> boolean isNullable = expressionType.isNullable() || safe;
> ...
> } {code}
>
> The same: _targetType.isNullable()_ is ignored.
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