SQL Query Builder

Tables: orders(id, customer_id, total, created_at), customers(id, name, email). Need: Top 10 customers by total spend in last 90 days with their order count.

## SQL Query\n\n```sql\nSELECT \n c.id,\n c.name,\n c.email,\n COUNT(o.id) AS order_count,\n SUM(o.total) AS total_spend\nFROM customers c\nINNER JOIN orders o ON c.id = o.customer_id\nWHERE o.created_at >= DATEADD(day, -90, GETDATE())\nGROUP BY c.id, c.name, c.email\nORDER BY total_spend DESC\nLIMIT 10;\n```\n\n**Query Explanation:**\n- INNER JOIN connects customers to their orders\n- WHERE filters to last 90 days\n- GROUP BY aggregates per customer\n- ORDER BY + LIMIT gets top 10\n\n**Performance Tips:**\n- Add index on orders(customer_id, created_at)\n- Consider partitioning orders table by date\n\n**PostgreSQL variant:**\nReplace `DATEADD(day, -90, GETDATE())` with `CURRENT_DATE - INTERVAL 90 days`