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https://issues.apache.org/jira/browse/CALCITE-452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14196448#comment-14196448
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Julian Hyde commented on CALCITE-452:
-------------------------------------
Makes sense. I think it's reasonable to expect people to implement equals and
hashCode. We don't require/expect them to implement compareTo or Comparable
because SQL doesn't have a "default ordering" of the rows of a relation.
Can you commit this? But please wait until the big CALCITE-296 code re-org is
checked into master.
> JavaRowFormat.comparer relies on proper equals/compareTo in custom row classes
> ------------------------------------------------------------------------------
>
> Key: CALCITE-452
> URL: https://issues.apache.org/jira/browse/CALCITE-452
> Project: Calcite
> Issue Type: Bug
> Affects Versions: 0.9.1
> Reporter: Vladimir Sitnikov
> Assignee: Julian Hyde
> Priority: Minor
>
> When reviewing CALCITE-397 I noted that the fix was "convert to the target
> row type, then perform distinct".
> I wondered: why don't we perform distinct first, then convert row types? That
> might be much more efficient if the distinct reduces the number of rows
> dramatically, so we do not spend time on conversion.
> When I did tried this change, I noticed Calcite uses "default
> equals/compareTo".
> Not sure what is the best approach here: raise errors in such cases, create
> synthetic equals/hashCode/compareTo somehow, or reconvert to the type with
> proper comparison methods.
> Here's the change to use "distinct, then convert to the target physType":
> {code:java}
> Expressions.return_(
> null,
> + inputPhysType.convertTo(
> Expressions.call(
> + childExp,
> - inputPhysType.convertTo(childExp, physType),
> BuiltinMethod.DISTINCT.method,
> Expressions.<Expression>list()
> .appendIfNotNull(inputPhysType.comparer()))
> + , physType)
> ));
> {code}
> The generated java code is as following (note how {{.distinct()}} is used
> over {{JdbcTest$Employee}} that has no {{equals/compareTo}} methods):
> {code:java}
> /* 3 */ public net.hydromatic.linq4j.Enumerable bind(final
> net.hydromatic.optiq.DataContext root0) {
> /* 4 */ root = root0;
> /* 5 */ return
> net.hydromatic.linq4j.Linq4j.asEnumerable(((net.hydromatic.optiq.test.JdbcTest.HrSchema)
> ((net.hydromatic.optiq.impl.java.ReflectiveSchema)
> root.getRootSchema().getSubSchema("hr").unwrap(net.hydromatic.optiq.impl.java.ReflectiveSchema.class)).getTarget()).emps).distinct().select(new
> net.hydromatic.linq4j.function.Function1() {
> /* 6 */ public Object[]
> apply(net.hydromatic.optiq.test.JdbcTest.Employee o) {
> /* 7 */ return new Object[] {
> /* 8 */ o.empid,
> /* 9 */ o.deptno,
> /* 10 */ o.name,
> /* 11 */ o.salary,
> /* 12 */ o.commission};
> /* 13 */ }
> /* 14 */ public Object apply(Object o) {
> /* 15 */ return apply(
> /* 16 */ (net.hydromatic.optiq.test.JdbcTest.Employee) o);
> /* 17 */ }
> /* 18 */ }
> /* 19 */ );
> /* 20 */ }
> {code}
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