[Solved] What is the problem with this query?SELECT employee_id, (SELECT department_name FROM departments) AS dept FROM employees;Assuming departments contains multiple rows. | SQL

SQL - Subqueries

What is the problem with this query?

SELECT employee_id, (SELECT department_name FROM departments) AS dept FROM employees;
Assuming departments contains multiple rows.

AThe query will return NULL for all employees

BThe scalar subquery returns multiple rows causing an error

CThe subquery is missing a GROUP BY clause

DThe query will execute successfully without issues

Step-by-Step Solution

Solution:

Step 1: Analyze the subquery
The subquery (SELECT department_name FROM departments) returns multiple rows because no WHERE clause limits it.
Step 2: Scalar subquery requirement
A scalar subquery must return exactly one value (one row, one column).
Step 3: Resulting error
Since multiple rows are returned, the query will raise an error.
Final Answer:
The scalar subquery returns multiple rows causing an error -> Option B
Quick Check:
Scalar subqueries must return one value only [OK]

Quick Trick: Scalar subquery must return single value [OK]

Common Mistakes:

MISTAKES

Ignoring multiple rows returned by subquery
Assuming subquery returns NULL instead of error
Not correlating subquery with outer query

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What is the problem with this query?

Step 1: Analyze the subquery

Step 2: Scalar subquery requirement

Step 3: Resulting error

Final Answer:

Quick Check:

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