[CALCITE-3221] Add MergeUnion operator in Enumerable convention

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.19.0
• Fix Version/s: 1.27.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Ruben Q L
• Reporter: Stamatis Zampetakis
• Created: 31/Jul/19 15:25
• Updated: 08/Feb/22 12:07
• Resolved: 10/Feb/21 08:40

Description

Currently, the union operation offered by Calcite (see EnumerableDefaults.union) "breaks" the collation (if any) of its inputs.

The goal of this issue is to create a new union algorithm in Enumerable convention (EnumerableMergeUnion) that, given the fact that its inputs are sorted by the same collation, will return the union / union all result respecting this collation.

Most likely the implementation of the merge join can be useful.

Issue Links

• blocks: CALCITE-4017 Implement trait propagation for Enumerable Setop
• is related to: CALCITE-5003 MergeUnion on types with different collators produces wrong result
• is related to: CALCITE-4021 EnumerableUnion should preserve ordering when all inputs have the same collation
• relates to: CALCITE-4480 Make EnumerableDefaults#union a non-blocking operation
• links to: GitHub Pull Request #2329