What does ISNULL(price, 50) return if price is NULL?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of SQL & Databases conventions, runtime behavior, and memory/performance considerations.
02
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
If price is NULL, ISNULL(price, 50) evaluates to 50.
### Function Nuances Across Databases:
- SQL Server:
ISNULL(check_expression, replacement_value)returns the replacement if the first argument is NULL. - MySQL:
ISNULL(expr)returns a boolean1(true) or0(false). For value substitution, MySQL usesIFNULL(price, 50). - ANSI Standard Portable Solution (
COALESCE):
The ANSI standard function supported across all SQL databases (PostgreSQL, MySQL, Oracle, SQLite, SQL Server) is COALESCE:
SELECT COALESCE(price, 50) AS effective_price FROM products;
COALESCE accepts two or more arguments and returns the very first non-NULL value.
Candidate Response Strategy & Interview Tips
- 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.