問74
頻出度★★☆
“気温”表の2011年の7月1日から8月31日までの間で，最高気温が35度以上のレコードを全て抽出したい。抽出条件として，適切なものはどれか。 気温
| 年 | 月 | 日 | 最高気温 |
|---|---|---|---|
| 2011 | 1 | 1 | 12 |
| 2011 | 1 | 2 | 11 |
| 2011 | 1 | 3 | 9 |
| ： | ： | ： | ： |
| 2011 | 7 | 31 | 34 |
| 2011 | 8 | 1 | 36 |
| ： | ： | ： | ： |
| 2011 | 12 | 31 | 10 |
| 2012 | 1 | 1 | 11 |
平成28年度 秋期 ITパスポート試験 問74
テクノロジ系データベース › データ操作
This question's explanation and your answers so far.
解説
問 74
Incorrectア
The month condition is (Month = 7 and Month = 8), but a single record's month can never be both 7 and 8 at the same time, so the parentheses are always false and not a single record is extracted. In addition, Max temperature ≦ 35 means “35 degrees or lower”, the opposite of the required “35 degrees or higher”. Wrong on two counts.
Incorrectイ
Max temperature ≧ 35 is correct, but the month condition (Month = 7 and Month = 8) uses and, and no record is both July and August at once, so the result is empty. To collect both July and August, or is required.
Incorrectウ
The month condition (Month = 7 or Month = 8) is correct, but Max temperature ≦ 35 means “35 degrees or lower”, the opposite of the required “35 degrees or higher”, so it picks up records on the low-temperature side.
- エ
正解 The records to extract are those satisfying all three conditions: “2011”, “July 1 to August 31”, and “max temperature 35 degrees or higher”. Choice エ is Year = 2011 and (Month = 7 or Month = 8) and Max temperature ≧ 35, which correctly expresses these three conditions. The key point is how the month is specified: since each record has only one month value, to collect both the July and August records you must join them with or as “Month = 7 or Month = 8”. Also, “35 degrees or higher” includes 35 and extends upward, so Max temperature ≧ 35 is correct. Therefore エ is appropriate.
ここがポイント
- When a range is specified as “matches any one of them”, use or; when “both must hold at the same time”, use and. Since one field of a single record can never hold multiple values at once, joining mutually exclusive values such as Month = 7 and Month = 8 with and always yields an empty set.
- “Or higher (以上)” includes the boundary value and extends upward (≧); “or lower (以下)” includes the boundary value and extends downward (≦). Map the wording of the condition correctly to the comparison operator.
用語