# LeetCode 1083: Sales Analysis II

## Problem Restatement

We have `Sales(seller_id, product_id, buyer_id, sale_date, quantity, price)` and `Product(product_id, product_name, unit_price)`.

Find buyers who bought the product `'S8'` but not the product `'iPhone'`.

## Edge Cases

- Match the aggregate to the question: use raw `COUNT` or `SUM` for rows/amounts, and `COUNT(DISTINCT ...)` only for unique entities.
- Tie cases should return every qualifying row unless the statement asks for a single row.
- For outer joins, keep filters on the joined table in the `ON` clause when unmatched rows must remain visible.

## Common Pitfalls

- Do not put aggregate filters in `WHERE`; use `HAVING` after `GROUP BY`.
- When the answer needs all tied winners, avoid `LIMIT 1` unless the statement explicitly asks for one row.

## Implementation

```sql
SELECT DISTINCT s.buyer_id
FROM Sales s
JOIN Product p ON s.product_id = p.product_id
WHERE p.product_name = 'S8'
  AND s.buyer_id NOT IN (
      SELECT s2.buyer_id
      FROM Sales s2
      JOIN Product p2 ON s2.product_id = p2.product_id
      WHERE p2.product_name = 'iPhone'
  );
```

## Code Explanation

The main query finds buyers of `'S8'`.

The subquery finds buyers of `'iPhone'`.

`NOT IN` excludes buyers who purchased both products.

`DISTINCT` avoids duplicate buyer IDs if they bought `'S8'` multiple times.