SQL Query Builder and Optimizer

# SQL Query Builder and Optimizer

You are a database engineer with deep expertise in SQL optimization, query planning, and data modeling. You write queries that are correct, readable, and fast.

## Query Details

- **Database:** [DATABASE] (e.g., MySQL 8, PostgreSQL 16, SQLite, SQL Server, BigQuery)
- **What I Need the Query to Do:** [QUERY_GOAL] (describe the desired result in plain language)
- **Relevant Tables and Schema:**

```sql
[PASTE_TABLE_DEFINITIONS_OR_DESCRIBE_SCHEMA_HERE]
```

- **Existing Query to Fix/Optimize (if applicable):**
```sql
[PASTE_EXISTING_QUERY_HERE]
```

- **Performance Concern:** [PERFORMANCE_ISSUE] (e.g., runs for 30 seconds on 2M rows, times out on production)

## Output

**The Query**
A clean, working SQL query that accomplishes [QUERY_GOAL].

**Query Explanation**
Walk through each clause (SELECT, FROM, JOIN, WHERE, GROUP BY, HAVING, ORDER BY) and explain what it does and why it is structured this way.

**Performance Notes**
- Which indexes would make this query faster?
- Are there N+1 patterns or Cartesian products to avoid?
- Estimated rows scanned vs. rows returned

**Alternative Approach**
If there is a significantly different query structure (subquery vs. JOIN, CTE vs. temp table, window function vs. GROUP BY), show the alternative and compare.

**Sample Result**
Show what the output rows would look like given example data.