fix(plan): dedup update from source matches

[ck89119]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #23137

What this PR does / why we need it:

This PR fixes the PostgreSQL-style UPDATE ... SET ... FROM ... WHERE ... path when duplicate source rows match the same target row on tables without FK constraints.

The new UPDATE path previously fed duplicate joined rows directly into the update pipeline, which could materialize duplicate primary-key rows for one target row. This change adds a planner-side dedup step for UPDATE ... FROM: group by the target row's original columns and use any_value() for updated columns, matching the existing fallback path behavior.

Test coverage includes:

• A planner unit test that asserts the new UPDATE path produces AGG + any_value dedup.
• A BVT case without FK constraints that verifies duplicate source matches still leave each target primary key with exactly one row.

Tested with:

• git diff --check
• go test ./pkg/sql/plan -run TestUpdatePgStyleFromDedupsDuplicateSourceMatchesOnNewPath -count=1
• go test ./pkg/sql/plan -count=1
• mo-tester update_pg_style_from.sql (108/108 passed)
• make
• make static-check (0 issues)

[qodo-code-review]

Qodo reviews are paused for this user.

Troubleshooting steps vary by plan Learn more →

On a Teams plan?
Reviews resume once this user has a paid seat and their Git account is linked in Qodo.
Link Git account →

Using GitHub Enterprise Server, GitLab Self-Managed, or Bitbucket Data Center?
These require an Enterprise plan - Contact us
Contact us →