This question's explanation and your answers so far.
関係データベースで管理された“商品”表，“売上”表から売上日が5月中で，かつ，商品ごとの合計額が20,000円以上になっている商品だけを全て挙げたものはどれか。 商品
| 商品コード | 商品名 | 単価（円） |
|---|---|---|
| 0001 | 商品A | 2,000 |
| 0002 | 商品B | 4,000 |
| 0003 | 商品C | 7,000 |
| 0004 | 商品D | 10,000 |
売上
| 売上番号 | 商品コード | 個数 | 売上日 | 配達日 |
|---|---|---|---|---|
| Z00001 | 0004 | 3 | 4/30 | 5/2 |
| Z00002 | 0001 | 3 | 4/30 | 5/3 |
| Z00005 | 0003 | 3 | 5/15 | 5/17 |
| Z00006 | 0001 | 5 | 5/15 | 5/18 |
| Z00003 | 0002 | 3 | 5/5 | 5/18 |
| Z00004 | 0001 | 4 | 5/10 | 5/20 |
| Z00007 | 0002 | 3 | 5/30 | 6/2 |
| Z00008 | 0003 | 1 | 6/8 | 6/10 |
This includes Product A, which is wrong. Product A's May portion is 2,000 yen×(5 units+4 units) = 18,000 yen, which is less than 20,000 yen, so it does not satisfy the condition. If you also count the 4/30 (April) sale, or read the 20,000-yen “or more” boundary too loosely, you would mistakenly include it.
Product B and Product C are correct, but including Product A and Product D is wrong. Product A's May portion is 18,000 yen, less than 20,000 yen. Product D has no sales date in May (its only sale is 4/30, which is April), so its aggregated amount is 0 yen. Not filtering by sales date, or confusing it with the delivery date (5/2), leads to the typical mistake of including Product D.
正解 There are two conditions: the “sales date is within May”, and the “total amount per product (the sum of unit price × quantity) is 20,000 yen or more”. First, extract from the Sales table only the rows whose sales date is in May. Since 4/30 is April and 6/8 is June, the three rows Z00001, Z00002, and Z00008 are excluded. The remaining rows are Z00005 (Product C, 3 units), Z00006 (Product A, 5 units), Z00003 (Product B, 3 units), Z00004 (Product A, 4 units), and Z00007 (Product B, 3 units). Next, summing unit price × quantity per product: Product A = 2,000×(5+4) = 18,000 yen, Product B = 4,000×(3+3) = 24,000 yen, Product C = 7,000×3 = 21,000 yen, and Product D has no May sales, so 0 yen. Only Product B and Product C satisfy 20,000 yen or more, so the correct answer is ウ.
This misses Product B. Product B has two records, 5/5 (Z00003) and 5/30 (Z00007), each with 3 units, giving 4,000 yen×(3+3) = 24,000 yen, which satisfies 20,000 yen or more. Misreading 5/30 as June, or overlooking the rows with product code 0002, leaves only Product C.