Select the statement for the query that lists the cities that do not have a department located in them. Be sure to select the syntactically correct statement.

Question

BlackTom AI · Accepted Answer

NOT EXISTS returns rows for which the correlated subquery returns no rows, so it is the correct construct to list cities that do NOT have a department.

1) Relevant concepts
- EXISTS/NOT EXISTS: EXISTS(...) is true when the subquery returns at least one row; NOT EXISTS(...) is true when it returns zero rows.  
- Correlated subquery: the inner query references a value from the outer query (here o1.location_id) to test each outer row.  
- JOIN inside subquery: allowed, but the correlation must correctly compare the inner result to the outer row.

2) Step-by-step reasoning
- We want every city in locations for which there is no department whose location_id equals that location’s id.  
- For each outer row (locations as o1), run the subquery that attempts to find any matching department. If the subquery finds any matching row, EXISTS is true and the outer row should be excluded; if the subquery finds none, NOT EXISTS is true and the outer city should be returned.

3) How the given query works (showing correlation)
SELECT o1.city
FROM locations as o1
WHERE NOT EXISTS
  (SELECT *
   FROM locations as i1 INNER JOIN departments as id
     ON i1.location_id = id.location_id
   WHERE o1.location_id = id.location_id);

- The inner JOIN produces department rows linked to location rows (i1).  
- The WHERE o1.location_id = id.location_id correlates the subquery to the outer row.  
- If no id row matches o1.location_id, subquery returns zero rows → NOT EXISTS is true → city included.

4) Why this answer is correct
- It uses NOT EXISTS (necessary for "do not have") and places the correlation in the subquery WHERE clause, which is the standard, syntactically correct way to write a correlated NOT EXISTS check.

5) Why other options are incorrect (brief)
- Variants with WHERE EXISTS would return cities that DO have departments (opposite).  
- Variants that put the correlation only inside the ON clause or use a NATURAL JOIN may be syntactically or semantically incorrect as a correlated subquery (correlation should be expressed in the subquery’s WHERE for clear portability), or may change logic.

Conclusion: The provided statement using NOT EXISTS with the correlated subquery is correct and matches the supplied answer.

Select the statement for the query that lists the cities that do not have a department located in them. Be sure to select the syntactically correct statement. 单项选择题

类似问题

In the database redesign process, an SQL tool that is useful for testing whether certain conditions or assumptions are valid is ________.

You own a bond that pays $64 in interest annually. The face value is $1,000 and the current market price is $1,021.61. The bond matures in 11 years. What is the yield to maturity?

Which of the following statements is CORRECT?

It will cost $9,600 to acquire an ice cream cart that is expected to produce cash inflows of $3,600 a year for three years. After the three years, the cart is expected to be worthless. What is the payback period?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单