---
phase: 03-expansion-engine
plan: "02"
subsystem: database
tags: [sql-generation, join-resolution, fuzzy-matching, strsim, levenshtein, tdd]

# Dependency graph
requires:
  - phase: 03-expansion-engine
    plan: "01"
    provides: "expand() function, QueryRequest, ExpandError, quote_ident(), source_table field"
provides:
  - "Join dependency resolution with source_table-based pruning"
  - "Transitive join dependency resolution via fixed-point loop"
  - "Name validation with fuzzy 'did you mean' suggestions (strsim)"
  - "suggest_closest() helper using Levenshtein distance"
  - "resolve_joins() function for join pruning"
affects: [03-03 (proptest PBT), 04-query-interface]

# Tech tracking
tech-stack:
  added: [strsim 0.11]
  patterns: [fuzzy-matching-levenshtein, fixed-point-join-resolution, source-table-join-pruning]

key-files:
  created: []
  modified: [src/expand.rs, Cargo.toml]

key-decisions:
  - "Levenshtein threshold of 3 for fuzzy suggestions; balances helpfulness vs false positives"
  - "ON-clause substring matching for transitive join dependency detection; sufficient heuristic for v0.1"
  - "Join resolution uses fixed-point loop for convergence; handles arbitrary transitive depth"
  - "Case-insensitive matching for source_table lookups (consistent with dimension/metric matching)"

patterns-established:
  - "resolve_joins() extracts join pruning logic from expand() for testability"
  - "suggest_closest() reusable for any name-to-candidates fuzzy matching"
  - "Fixed-point loop pattern for transitive dependency resolution"

requirements-completed: [MODEL-03, EXPAND-02, EXPAND-03, TEST-01]

# Metrics
duration: 4min
completed: 2026-02-25
---

# Phase 3 Plan 02: Join Resolution and Fuzzy Matching Summary

**Join dependency resolution with source_table pruning and strsim-powered fuzzy "did you mean" suggestions -- 13 new tests via TDD (27 total in expand module)**

## Performance

- **Duration:** 4 min
- **Started:** 2026-02-24T23:48:06Z
- **Completed:** 2026-02-24T23:52:07Z
- **Tasks:** 2
- **Files modified:** 2

## Accomplishments
- Join pruning: only joins needed by requested dimensions/metrics are included in the CTE
- Transitive join dependencies resolved automatically (if regions.ON references customers, customers is included)
- Fuzzy "did you mean" suggestions for misspelled dimension/metric names using Levenshtein distance
- Duplicate dimension/metric name detection with clear error messages
- 13 new unit tests via TDD (7 validation + 7 join resolution, minus 1 replaced Plan 01 test)

## Task Commits

Each task was committed atomically:

1. **Task 1: Name validation with fuzzy matching** - `5bd6de9` (feat)
2. **Task 2: Join dependency resolution** - `a43d240` (feat)

_Note: Both tasks follow TDD with RED (failing tests) then GREEN (implementation) in a single commit each_

## Files Created/Modified
- `src/expand.rs` - Added suggest_closest(), resolve_joins(), name validation, join pruning; 13 new tests
- `Cargo.toml` - Added strsim 0.11 dependency

## Decisions Made
- Levenshtein threshold of 3 for fuzzy suggestions: close enough for typos (reigon -> region), but not for completely unrelated names (xyzzy -> None)
- Transitive join resolution uses ON-clause substring matching: if regions.ON contains "customers", customers is a dependency. This is a heuristic but sufficient for v0.1 where join ON clauses are opaque SQL strings
- Fixed-point loop for convergence: handles chains of any depth (A -> B -> C)
- Replaced Plan 01's test_joins_included_in_cte (which tested "include all joins") with targeted join resolution tests

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered
None

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- expand() now has complete name validation, join resolution, and SQL generation
- Ready for Plan 03 to add proptest property-based tests
- All 27 expand tests + 7 model tests pass (34 total, excluding pre-existing sandbox-blocked catalog tests)

## Self-Check: PASSED

- FOUND: src/expand.rs
- FOUND: Cargo.toml (modified)
- FOUND: commit 5bd6de9 (Task 1 - name validation with fuzzy matching)
- FOUND: commit a43d240 (Task 2 - join dependency resolution)
- FOUND: 03-02-SUMMARY.md

---
*Phase: 03-expansion-engine*
*Completed: 2026-02-25*
