IEJoin (range join) index out of bounds on empty result

[TCeason]

Summary

• Location: src/query/service/src/pipelines/processors/transforms/range_join/ie_join_state.rs:483
• Panic message: index out of bounds: the len is 0 but the index is 0

Likely trigger files

DuckDB source: test/sql/join/iejoin/iejoin_issue_6861.test
Converted file: sql/join/iejoin/iejoin_issue_6861.test

This file has an active query on an empty table with a BETWEEN range join:

CREATE TABLE test(x INT);
-- table is empty at this point
SELECT * FROM test AS a, test AS b WHERE (a.x BETWEEN b.x AND b.x);

Other iejoin files with gate=fail may also trigger this:

• test/sql/join/iejoin/iejoin_issue_7278.test
• test/sql/join/iejoin/test_iejoin_null_keys.test (LEFT JOIN with inequality, nullable output)
• test/sql/join/iejoin/test_iejoin_east_west.test

Reproduction

The call chain is:

TransformRangeJoinLeft::process (transform_range_join.rs:138)
  → RangeJoinState::ie_join (ie_join_state.rs:183)
    → RangeJoinState::fill_outer (ie_join_state.rs:483)  ← PANIC

Triggered by a range join (inequality join) query where one side produces zero rows. The fill_outer method indexes into an empty Vec<DataBlock> at position 0.

Key stack frames

#	Function	File
14	RangeJoinState::fill_outer	ie_join_state.rs:483
15	RangeJoinState::ie_join	ie_join_state.rs:183
16	TransformRangeJoinLeft::process	transform_range_join.rs:138

Root cause

fill_outer does self.xxx[0] without checking if the vec is empty. Empty input is a valid edge case for outer joins.

Fix direction

Guard the index access with an emptiness check, or return an empty DataBlock directly when input is empty.