Which one uses an inline view?

Question

BlackTom AI · Accepted Answer

An inline view (also called a derived table) is a subquery placed in the FROM clause; the database treats its result set like a temporary table that you can reference with an alias in the outer query.

1) Relevant knowledge points and concepts
- Inline view / derived table: subquery in FROM, requires an alias, behaves like a table.
- Subqueries in WHERE or SELECT: not inline views; they supply values (scalar, set) to filter or compute.
- GROUP BY queries can be simple aggregations and may contain no subqueries at all.

2) Step-by-step reasoning examining each choice
Option A:
SELECT name FROM employees
WHERE salary = (
  SELECT MAX(salary)
  FROM employees
);
- The subquery appears in the WHERE clause and returns a scalar (MAX). That is a scalar subquery, not an inline view.

Option B:
SELECT department_id, AVG(salary)
FROM employees
GROUP BY department_id;
- No subquery anywhere. This is a plain aggregation query, not an inline view.

Option C:
SELECT name FROM employees
WHERE salary IN (
  SELECT salary FROM job_history
);
- The subquery is in the WHERE clause and returns a set for the IN operator. This is a subquery in WHERE, not an inline view.

Option D:
SELECT e.name
FROM (
  SELECT * FROM employees
  WHERE department_id = 50
) e
WHERE e.salary > 50000;
- The subquery is inside the FROM clause, enclosed in parentheses, and given the alias e. The outer query selects from that derived table e. This matches the definition of an inline view (derived table).

3) Intermediate steps / verification
- Check placement: only Option D places the subquery in FROM.
- Check alias: Option D uses alias e, required to reference the inline view.

4) Why the correct answer is correct
- Option D implements a FROM (subquery) ... alias pattern, so the subquery's result is used as a temporary table (inline view) for further filtering (WHERE e.salary > 50000).

5) Why other options are incorrect (brief)
- A and C: subqueries are in WHERE (scalar or set), not in FROM.
- B: contains no subquery.

6) Conclusion
The correct answer is the query in Option D:
SELECT e.name
FROM (
  SELECT * FROM employees
  WHERE department_id = 50
) e
WHERE e.salary > 50000;
This matches the provided answer.

Which one uses an inline view?单项选择题

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