Diagnose Slow SQL Queries with EXPLAIN ANALYZE & Composite Index Tuning via AI

Act as a Principal Database Administrator (MySQL 8.0 / PostgreSQL 16).
I have a slow query taking [X] seconds on a table with [X] million rows.
1) **Slow SQL**:
```sql
[Paste SQL]
```
2) **Table Schema & Indexes (`SHOW CREATE TABLE`)**:
```sql
[Paste DDL]
```
3) **`EXPLAIN ANALYZE` Output**:
```text
[Paste EXPLAIN]
```
Provide:
1) [Execution Plan Breakdown]: Explain why the optimizer chose this plan and why index invalidation, `Using filesort`, or `Using temporary` occurred;
2) [Optimal Composite Index DDL]: Exact `CREATE INDEX` statement following ESR (Equality, Sort, Range) rules, plus redundant existing indexes safe to drop;
3) [High-Performance SQL Rewrite]: Equivalent query using deferred joins, CTEs or `EXISTS` for sub-50ms execution.