Explain how NULL affects comparisons, sorting, and aggregates. How do you handle it safely?

Problem Statement

Explanation

NULL means unknown. Comparisons like col = NULL are unknown, so conditions fail. Use IS NULL and IS NOT NULL. Sort order places NULLs either first or last depending on the engine or explicit NULLS FIRST or LAST. Aggregates skip NULLs except COUNT(*). Use COALESCE to substitute defaults, and design constraints to avoid surprise NULLs where business rules require values.

Code Solution

SolutionRead Only

SELECT COALESCE(phone,'N/A') AS phone
FROM users
ORDER BY phone NULLS LAST;

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This question appears in the following practice sets:

SQL Core Fundamentals

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Explain how NULL affects comparisons, sorting, and aggregates. How do you handle it safely?

Problem Statement

Explanation

Code Solution

Practice Sets

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Master Interviews Anywhere, Anytime

Explain how NULL affects comparisons, sorting, and aggregates. How do you handle it safely?

Problem Statement

Explanation

Code Solution

Practice Sets

Related Questions

Which SQL statement retrieves all columns and rows from a table named employees?

Which clause filters rows before aggregation and affects which rows are grouped?

What is the default sort order when ORDER BY is used without ASC or DESC?

Which construct is commonly used to paginate results in SQL engines like Postgres and MySQL?

Which predicate correctly checks for missing values in standard SQL?

More from SQL & Databases

Master Interviews
Anywhere, Anytime