[Bug] UNION ALL query return wrong empty set

[ccoffline]

Describe the bug

-- create table
DROP TABLE IF EXISTS `test_t`;
CREATE TABLE `test_t` (
 `name` VARCHAR(1000) NULL COMMENT "string"
) ENGINE=OLAP
DUPLICATE KEY(`name`)
DISTRIBUTED BY HASH(`name`) BUCKETS 5
PROPERTIES (
"replication_num" = "1",
"in_memory" = "false",
"storage_format" = "DEFAULT"
);

-- insert data
INSERT INTO test_t (`name`)
VALUES ('aaaaa'), ('ccccc')
;

-- returns wrong empty set
SELECT `t1`.`name`
FROM (
 SELECT `name`
 FROM `test_t`
GROUP BY `name`
 ) `t1`
UNION ALL
SELECT `t2`.`name`
FROM (
 SELECT `name`,
 -1 as `bool`
 FROM `test_t`
GROUP BY `name`
 ) `t2`
WHERE `t2`.`bool` = 1
;

-- returns correct result ‘aaaaa’ and ‘ccccc’
SELECT `t2`.`name`
FROM (
 SELECT `name`,
 -1 as `bool`
 FROM `test_t`
GROUP BY `name`
 ) `t2`
WHERE `t2`.`bool` = 1
UNION ALL
SELECT `t1`.`name`
FROM (
 SELECT `name`
 FROM `test_t`
GROUP BY `name`
 ) `t1`
;

Additional context
Fixing, may need some help QAQ.

[ccoffline]

This bug is caused by #4206's fix #4235, scanNodes.clear() here remove all previous scanNodes if the last statement is considered to return an empty set.
https://github.com/apache/incubator-doris/blob/a61eea3b2e76d741c98b9faed8cec51c1d469f94/fe/fe-core/src/main/java/org/apache/doris/planner/SingleNodePlanner.java#L284-L290

[kangkaisen]

I forget to submit a PR to the Github master branch.
You could change the code to, and submit a PR.

 if (analyzer.hasEmptyResultSet()) {
 List<TupleId> scanTupleIds = root.getAllScanTupleIds();
 PlanNode node = createEmptyNode(stmt, analyzer);
 // Ensure result exprs will be substituted by right outputSmap
 node.setOutputSmap(root.outputSmap);

 // Must and could only remove the scanNode that the tuple id is same with EmptyNode,
 // otherwise we will get NPE in Coordinator::computeScanRangeAssignment
 scanNodes.removeIf(scanNode -> scanTupleIds.contains(scanNode.getTupleIds().get(0)));
 // Currently, getMaterializedTupleIds for AnalyticEvalNode is wrong,
 // So we explicitly add AnalyticEvalNode tuple ids to EmptySetNode
 if (root instanceof AnalyticEvalNode) {
 node.getTupleIds().addAll(root.tupleIds);
 }
 return node;
 }

[ccoffline]

I forget to submit a PR to the Github master branch.
You could change the code to, and submit a PR.

 if (analyzer.hasEmptyResultSet()) {
 List<TupleId> scanTupleIds = root.getAllScanTupleIds();
 PlanNode node = createEmptyNode(stmt, analyzer);
 // Ensure result exprs will be substituted by right outputSmap
 node.setOutputSmap(root.outputSmap);

 // Must and could only remove the scanNode that the tuple id is same with EmptyNode,
 // otherwise we will get NPE in Coordinator::computeScanRangeAssignment
 scanNodes.removeIf(scanNode -> scanTupleIds.contains(scanNode.getTupleIds().get(0)));
 // Currently, getMaterializedTupleIds for AnalyticEvalNode is wrong,
 // So we explicitly add AnalyticEvalNode tuple ids to EmptySetNode
 if (root instanceof AnalyticEvalNode) {
 node.getTupleIds().addAll(root.tupleIds);
 }
 return node;
 }

I can't find method getAllScanTupleIds in PlanNode root

[kangkaisen]

@ccoffline Sorry. you could add this method to PlanNode:

 protected List<TupleId> getAllScanTupleIds() {
 List<TupleId> tupleIds = Lists.newArrayList();
 List<ScanNode> scanNodes = Lists.newArrayList();
 collectAll(Predicates.instanceOf(ScanNode.class), scanNodes);
 for(ScanNode node: scanNodes) {
 tupleIds.addAll(node.getTupleIds());
 }
 return tupleIds;
 }