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https://issues.apache.org/jira/browse/CALCITE-2129?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16484326#comment-16484326
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Atri Sharma commented on CALCITE-2129:
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[~julianhyde] I am hacking this and figured that when we see the subquery's
aggregate in RelToSqlConverter, we should let be created as an expression and
not add it to ordinal map. Does that seem like a reasonable rule, please?
> RelToSqlConverter incorrectly projects aggregate function from sub-query
> ------------------------------------------------------------------------
>
> Key: CALCITE-2129
> URL: https://issues.apache.org/jira/browse/CALCITE-2129
> Project: Calcite
> Issue Type: Bug
> Components: core, jdbc-adapter
> Affects Versions: 1.15.0
> Reporter: Paul Jackson
> Assignee: Atri Sharma
> Priority: Major
>
> Starting with this DDL:
> {code:SQL}
> create table friends (
> id int not null,
> friend_id int,
> primary key (id),
> foreign key (friend_id) references friends (id)
> );
> insert into friends values
> (210, null),
> (209, 210),
> (202, 209),
> (208, 202),
> (207, 209),
> (203, 207),
> (201, null),
> (204, null),
> (205, null),
> (206, 209);
> {code}
> This query gives the highest id of friends that share friend_id for each
> friend:
> {code:SQL}
> SELECT id, friend_id,
> (SELECT max(f2.id)
> FROM friends AS f2
> WHERE f2.friend_id = f1.friend_id) AS foaf_id
> FROM friends AS f1
> id friend foaf
> 201
> 202 209 207
> 203 207 203
> 204
> 205
> 206 209 207
> 207 209 207
> 208 202 208
> 209 210 209
> 210
> {code}
> I convert this query to a RelNode and then converted it back to SQL:
> {code:Java}
> Planner aPlanner = Frameworks.getPlanner(aConfig);
> SqlNode aQuery = aPlanner.parse(theSql);
> aQuery = aPlanner.validate(aQuery);
> RelNode aRelNode = aPlanner.rel(aQuery).project();
> RelToSqlConverter aSqlConverter = new RelToSqlConverter(aSqlDialect);
> SqlNode aSqlNode = aSqlConverter.visitChild(0, aRelNode).asStatement();
> {code}
> This gives the following plan and SQL:
> {code}
> LogicalProject(id=[$0], friend_id=[$1], foaf_id=[$2])
> LogicalProject(id=[$0], friend_id=[$1], EXPR$0=[$3])
> LogicalJoin(condition=[=($1, $2)], joinType=[left])
> JdbcTableScan(table=[[stardog, friends]])
> LogicalAggregate(group=[{0}], EXPR$0=[MAX($1)])
> LogicalProject(friend_id=[$1], id=[$0])
> LogicalProject(id=[$0], friend_id=[$1])
> LogicalFilter(condition=[IS NOT NULL($1)])
> JdbcTableScan(table=[[stardog, friends]])
> SELECT `friends`.`id`, `friends`.`friend_id`, MAX(`id`)
> FROM `stardog`.`friends`
> LEFT JOIN (SELECT `friend_id`, MAX(`id`)
> FROM `stardog`.`friends`
> WHERE `friend_id` IS NOT NULL
> GROUP BY `friend_id`) AS `t1` ON `friends`.`friend_id` = `t1`.`friend_id`
> {code}
> This is a bad conversion. The {{MAX(`id`)}} should not be repeated in the
> outer select. PostgreSQL will complain that the aggregating function requires
> a group by. MySQL returns the max id that has a non-null friend (208), that
> id's friend (202), and the max id of all rows (210):
> {code}
> id friend MAX(`id`)
> 208 202 210
> {code}
> I think the correct SQL should be:
> {code:SQL}
> SELECT `friends`.`id`, `friends`.`friend_id`, foaf_id
> FROM `stardog`.`friends`
> LEFT JOIN (SELECT `friend_id`, MAX(`id`) AS foaf_id
> FROM `stardog`.`friends`
> WHERE `friend_id` IS NOT NULL
> GROUP BY `friend_id`) AS `t1` ON `friends`.`friend_id` = `t1`.`friend_id`
> {code}
> There is code in {{SqlImplementor}} and {{RelToSqlConverter}} that uses an
> {{ordinalMap}} to track what functions are aliases as what identifiers. When
> the SQL is generated, the identifier is replaced with the function. If all
> that code is removed, this works as expected (using {{EXPR$0}} as the alias
> rather than {{foaf_id}}).
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