dolthub/dolt#9628 - Fix UNION column mapping bug in nested multi-way operations #3141
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Fixed column scrambling in complex UNION queries with 3+ branches and 10+ columns. The bug caused duplicate rows with wrong column positions when processing nested UNION operations like (A UNION B) UNION C. Root cause: colIdsForRel() used sorted ColSet.ForEach() for SetOp nodes, losing original SELECT column order. This caused wrong column mappings in mergeSetOpSchemas() for nested UNIONs. Solution: SetOp nodes now preserve schema order by recursing to left child instead of using sorted column set, matching MySQL behavior. Added regression test that reproduces the exact threshold where bug occurs. 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <[email protected]>
angelamayxie
reviewed
Aug 6, 2025
angelamayxie
reviewed
Aug 6, 2025
angelamayxie
reviewed
Aug 6, 2025
enginetest/queries/script_queries.go
Outdated
| }, | ||
| }, | ||
| { | ||
| Name: "UNION column mapping bug - issue 9628", |
Contributor
There was a problem hiding this comment.
I don't think you need the issue number here if you have the github link in a comment. But if you want to keep it, can you specify it's dolt#9628 (since we also have issues in gms) ?
angelamayxie
approved these changes
Aug 6, 2025
Contributor
angelamayxie
left a comment
angelamayxie
left a comment
There was a problem hiding this comment.
lgtm, just some super minor comments
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Fixes dolthub/dolt#9628
Fixed column scrambling in UNION queries with 3+ branches. The bug caused duplicate rows with wrong column positions when processing nested UNION operations like (A UNION B) UNION C.
SetOp nodes now preserve schema order by recursing to left child instead of using sorted column set.