# Phase 21 — SQL Query Plan Inspector

Based on Phase 20.

## Added
- **Explain** button in SQL editor toolbar. Uses selected SQL when present, otherwise editor SQL.
- Separate query-plan window showing MySQL `EXPLAIN` in table format or `EXPLAIN FORMAT=JSON`.
- Shows optimizer plan columns in the existing native result grid; JSON format is selectable and copyable.
- Displays diagnostic query duration and server errors.
- Limits analysis to SELECT/WITH statements, does not run `EXPLAIN ANALYZE` (which executes the query).
- Does not replace editor query results or add EXPLAIN to normal query history.

## Notes
- Requires an active connection and MySQL permissions to explain the query.
- `EXPLAIN` gives estimated plans, not actual execution metrics.
- Only a single SQL statement should be selected; multi-statement SQL is not supported in the plan inspector.
- Not built in Xcode or tested against a live MySQL server in this environment.