SQL Subqueries — Core Truths Which statement accurately describes a fundamental property of subqueries in SQL?

Introduction:
Subqueries allow a query to be nested within another query to compute intermediate results or conditions. Recognizing the relationship between the outer query and the inner subquery is essential for writing expressive SQL across many use cases, including filtering, correlation, and aggregation.

Given Data / Assumptions:

• A subquery is a query used inside another statement.
• SQL dialects support subqueries in several clauses.
• Subqueries commonly begin with SELECT.

Concept / Approach:
The defining trait of a subquery is the nesting of one query (the inner query) inside another (the outer query). Many problems solvable by subqueries can also be solved by joins or window functions, so it is incorrect to claim they cannot return equivalent results. Most subqueries indeed start with SELECT, and they can appear in WHERE, HAVING, FROM (as derived tables), and sometimes in the SELECT list.

Step-by-Step Solution:
Identify the outer query that consumes the inner result.Place the inner query in an appropriate clause (for example, WHERE IN (SELECT ...)).Ensure that the subquery returns the expected shape (scalar, row, or set) for its context.Test with equivalent join-based formulations if you need performance or clarity.

Verification / Alternative check:
Rewrite a subquery using joins or EXISTS/IN transforms and compare results to confirm equivalence in many typical cases.

Why Other Options Are Wrong:

• Cannot return the same result is false; joins can often replicate subquery logic.
• Does not start with SELECT is false; most subqueries do start with SELECT.
• All of the above is false because the previous statements are incorrect.
• Only in SELECT list is false; subqueries are widely used in WHERE and HAVING and more.

Common Pitfalls:
Forgetting result cardinality: scalar subqueries must return one value, while IN subqueries can return sets; mismatches cause errors.

Final Answer:
Involves the use of an inner and outer query.