---
phase: 34.1-close-ddl-gaps-vs-snowflake
plan: 03
subsystem: ddl
tags: [fan-trap, show-dimensions, metric-filtering, vtab, graph-traversal]

# Dependency graph
requires:
  - phase: 34.1-02
    provides: "SHOW SEMANTIC DIMENSIONS/METRICS/FACTS VTab pattern and parser handlers"
provides:
  - "SHOW SEMANTIC DIMENSIONS IN view FOR METRIC metric -- fan-trap-aware dimension filtering"
  - "show_semantic_dimensions_for_metric table function"
  - "pub(crate) visibility for ancestors_to_root and collect_derived_metric_source_tables"
affects: [documentation, examples]

# Tech tracking
tech-stack:
  added: []
  patterns: ["fan-trap-aware VTab filtering via LCA path analysis"]

key-files:
  created:
    - src/ddl/show_dims_for_metric.rs
    - test/sql/phase34_1_show_dims_for_metric.test
  modified:
    - src/expand.rs
    - src/parse.rs
    - src/ddl/mod.rs
    - src/lib.rs
    - test/sql/TEST_LIST

key-decisions:
  - "FOR METRIC detected inside ShowDimensions rewrite handler, not as separate DdlKind variant"
  - "Fan-trap filtering extracted into reusable helper rather than duplicating expand.rs logic"
  - "rewrite_show_dims_for_metric helper extracted to keep rewrite_ddl under clippy line limit"

patterns-established:
  - "Two-parameter VTab pattern: view_name + metric_name for contextual dimension filtering"
  - "pub(crate) visibility for expand.rs helpers enables VTab reuse without duplication"

requirements-completed: [DDL-07]

# Metrics
duration: 13min
completed: 2026-03-22
---

# Phase 34.1 Plan 03: SHOW SEMANTIC DIMENSIONS FOR METRIC Summary

**Fan-trap-aware SHOW SEMANTIC DIMENSIONS FOR METRIC via LCA path analysis reusing expand.rs graph helpers**

## Performance

- **Duration:** 13 min
- **Started:** 2026-03-22T12:56:23Z
- **Completed:** 2026-03-22T13:10:03Z
- **Tasks:** 2
- **Files modified:** 7

## Accomplishments
- SHOW SEMANTIC DIMENSIONS IN view FOR METRIC metric returns only fan-trap-safe dimensions
- Fan-trap direction logic exactly matches check_fan_traps in expand.rs (same LCA path analysis)
- Derived metrics resolve source tables transitively via collect_derived_metric_source_tables
- 7 sqllogictest scenarios covering single-table, fan-trap filtering, derived metrics, errors, case insensitivity

## Task Commits

Each task was committed atomically:

1. **Task 1: Add SHOW DIMS FOR METRIC parser detection, fan-trap-aware VTab, and registration** - `487b69f` (feat)
2. **Task 2: Add sqllogictest for SHOW DIMS FOR METRIC and run full test suite** - `9ce68e8` (test)

## Files Created/Modified
- `src/ddl/show_dims_for_metric.rs` - Fan-trap-aware VTab: filters dimensions by metric reachability
- `src/expand.rs` - Made ancestors_to_root and collect_derived_metric_source_tables pub(crate)
- `src/parse.rs` - Added FOR METRIC detection in ShowDimensions handler; extracted rewrite_show_dims_for_metric helper
- `src/ddl/mod.rs` - Added show_dims_for_metric module declaration
- `src/lib.rs` - Registered show_semantic_dimensions_for_metric table function
- `test/sql/phase34_1_show_dims_for_metric.test` - 7 test scenarios for fan-trap-aware dimension filtering
- `test/sql/TEST_LIST` - Added new test file to test runner list

## Decisions Made
- FOR METRIC detected inside the ShowDimensions rewrite handler rather than adding a separate DdlKind variant. The detection uses the existing 3-keyword prefix (SHOW SEMANTIC DIMENSIONS) then checks for trailing `FOR METRIC` after the view name. This avoids a 5-keyword prefix match that would interleave with IN.
- Fan-trap filtering helper (`is_dimension_reachable_for_metric`) implemented as a separate function in show_dims_for_metric.rs reusing `ancestors_to_root` and `collect_derived_metric_source_tables` from expand.rs. The card_map uses `Cardinality` directly (without relationship name) since SHOW only needs reachability, not error reporting.
- Extracted `rewrite_show_dims_for_metric` as a separate function to keep `rewrite_ddl` under the clippy `too_many_lines` limit.
- Fixed pre-existing clippy `match_same_arms` warning in `extract_ddl_name` by merging Drop/DropIfExists/Describe/AlterRename/AlterRenameIfExists arms.

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 1 - Bug] Fixed DDL syntax in test file**
- **Found during:** Task 2
- **Issue:** Plan's test file used `:= expr TYPE type` syntax, but body parser uses `alias.name AS expr` syntax (no TYPE keyword)
- **Fix:** Rewrote all CREATE SEMANTIC VIEW statements to use correct `alias.name AS expr` syntax
- **Files modified:** test/sql/phase34_1_show_dims_for_metric.test
- **Committed in:** 9ce68e8

**2. [Rule 1 - Bug] Fixed missing error message in sqllogictest**
- **Found during:** Task 2
- **Issue:** `statement error` blocks required expected error message text after `----` separator
- **Fix:** Added expected error messages for non-existent metric and view test cases
- **Files modified:** test/sql/phase34_1_show_dims_for_metric.test
- **Committed in:** 9ce68e8

**3. [Rule 3 - Blocking] Added test file to TEST_LIST**
- **Found during:** Task 2
- **Issue:** New test file not discovered by per-process sqllogictest runner (requires explicit listing in TEST_LIST)
- **Fix:** Added `test/sql/phase34_1_show_dims_for_metric.test` to `test/sql/TEST_LIST`
- **Files modified:** test/sql/TEST_LIST
- **Committed in:** 9ce68e8

**4. [Rule 3 - Blocking] Fixed clippy warnings blocking commit**
- **Found during:** Task 1
- **Issue:** Pre-commit hook runs clippy; three warnings: unused assignment, rewrite_ddl too many lines, uninlined format args, match_same_arms
- **Fix:** Extracted rewrite_show_dims_for_metric helper, inlined format args, merged match arms
- **Files modified:** src/parse.rs
- **Committed in:** 487b69f

---

**Total deviations:** 4 auto-fixed (2 bug fixes, 2 blocking)
**Impact on plan:** All auto-fixes necessary for correctness and build compliance. No scope creep.

## Issues Encountered
- DuckLake CI test fails in sandbox mode due to `/Users/paul/.cache/uv/sdists-v9/.git: Operation not permitted`. This is a sandbox restriction, not a code issue. Test passes when run outside sandbox.

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

## Next Phase Readiness
- Phase 34.1 is now complete (all 3 plans executed)
- All DDL gap commands implemented: ALTER SEMANTIC VIEW RENAME, SHOW SEMANTIC DIMENSIONS/METRICS/FACTS, SHOW SEMANTIC DIMENSIONS FOR METRIC
- Ready for next milestone phase (documentation, registry publishing, etc.)

## Self-Check: PASSED

- FOUND: src/ddl/show_dims_for_metric.rs
- FOUND: test/sql/phase34_1_show_dims_for_metric.test
- FOUND: commit 487b69f
- FOUND: commit 9ce68e8

---
*Phase: 34.1-close-ddl-gaps-vs-snowflake*
*Completed: 2026-03-22*
