Return number of records in Customers?

Peer-reviewed by HireXTech Technical Panel • Updated for 2025/2026 hiring • Editorial standards

Interviewer Expectations for this Question

Core Competency

Assesses fundamental understanding of SQL & Databases conventions, runtime behavior, and memory/performance considerations.

Evaluation Criteria

Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.

Comprehensive Model Answer Verified Solution

To return the total count of rows in the Customers table, use **COUNT(*)**:

SELECT COUNT(*) AS total_customers 
FROM Customers;

### COUNT(*) vs COUNT(column):

**COUNT(*)**: Counts every row in the table, regardless of whether individual columns contain NULL values.
COUNT(column_name): Counts only rows where column_name is not NULL. If 10 out of 100 rows have NULL email addresses, COUNT(email) returns 90.

Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.

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