---
phase: 45-alter-comment-get-ddl
plan: 02
subsystem: database
tags: [duckdb, vscalar, ddl-reconstruction, get-ddl]

requires:
  - phase: 45-01
    provides: ALTER SET/UNSET COMMENT parser and VTab infrastructure
  - phase: 43
    provides: COMMENT, SYNONYMS, PRIVATE model fields
provides:
  - render_create_ddl function for DDL reconstruction from stored definitions
  - GET_DDL('SEMANTIC_VIEW', 'name') scalar function
  - First VScalar implementation in the extension
affects: [future-ddl-extensions, documentation]

tech-stack:
  added: []
  patterns: [VScalar registration, DDL reconstruction]

key-files:
  created:
    - src/render_ddl.rs
    - src/ddl/get_ddl.rs
    - test/sql/phase45_get_ddl.test
  modified:
    - src/ddl/mod.rs
    - src/lib.rs
    - test/sql/TEST_LIST

key-decisions:
  - "render_create_ddl lives in src/render_ddl.rs (not feature-gated) so unit tests run under cargo test"
  - "VScalar wrapper lives in src/ddl/get_ddl.rs (extension feature-gated)"
  - "Legacy definitions with empty tables vec produce a clear error rather than best-effort reconstruction"
  - "Round-trip integration test uses manual re-execution since DuckDB has no dynamic EXECUTE"

patterns-established:
  - "VScalar pattern: separate render logic (always compiled) from VScalar wrapper (extension-gated)"
  - "DDL reconstruction follows body parser clause ordering: TABLES -> RELATIONSHIPS -> FACTS -> DIMENSIONS -> METRICS"

requirements-completed: [SHOW-07, SHOW-08]

duration: 90min
completed: 2026-04-11
---

# Phase 45-02: GET_DDL Scalar Function Summary

**GET_DDL('SEMANTIC_VIEW', 'name') reconstructs re-executable CREATE OR REPLACE DDL from stored definitions with all metadata annotations**

## Performance

- **Duration:** ~90 min (including interrupted background agent, manual completion)
- **Tasks:** 2
- **Files modified:** 6

## Accomplishments
- `render_create_ddl` function traverses all model fields (TABLES, RELATIONSHIPS, FACTS, DIMENSIONS, METRICS) with COMMENT, SYNONYMS, PRIVATE annotations and correct clause ordering
- 21 unit tests cover all field combinations, escaping edge cases, and error handling
- `GetDdlScalar` VScalar registered as first scalar function in the extension
- 10 sqllogictest integration cases including round-trip verification (SHOW-08)

## Task Commits

1. **Task 1: DDL reconstruction module with unit tests** - `109de00` (feat)
2. **Task 2: VScalar registration and integration tests** - `bc3205d` (feat)

## Files Created/Modified
- `src/render_ddl.rs` - DDL reconstruction logic with helpers (escape_single_quote, emit_comment, emit_synonyms, emit_tables, etc.)
- `src/ddl/get_ddl.rs` - GetDdlScalar VScalar implementation
- `src/ddl/mod.rs` - Added pub mod get_ddl
- `src/lib.rs` - GET_DDL scalar function registration
- `test/sql/phase45_get_ddl.test` - 10 integration test cases
- `test/sql/TEST_LIST` - Added phase45_get_ddl.test

## Decisions Made
- Separated render logic (render_ddl.rs, always compiled) from VScalar wrapper (ddl/get_ddl.rs, extension-gated) so unit tests work without extension feature
- Used manual re-execution for round-trip tests since DuckDB doesn't support dynamic EXECUTE

## Deviations from Plan
- Plan specified Task 1 as render logic only; background agent also created VScalar in Task 1 commit. Task 2 completed VScalar registration and integration tests manually after agent interruption.
- Fixed EXECUTE round-trip tests (Cases 6, 9) to use manual CREATE OR REPLACE instead of unsupported EXECUTE syntax

## Issues Encountered
- Background executor agent was killed due to concurrent process concerns. Task 2 completed manually inline.
- DuckDB doesn't support `EXECUTE (SELECT ...)` for dynamic SQL — round-trip tests rewritten to manually re-execute DDL

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

## Next Phase Readiness
- GET_DDL provides the DDL reconstruction needed for any future DDL export/migration features
- All v0.6.0 ALTER + introspection requirements (ALT-01, ALT-02, SHOW-07, SHOW-08) complete

---
*Phase: 45-alter-comment-get-ddl*
*Completed: 2026-04-11*
