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Relational Foundations
SELECT literals Column aliases DISTINCT rows ORDER BY LIMIT and OFFSET NULL semantics Three-valued logic CASE expressions COALESCE NULLIF
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WHERE predicates Comparison operators BETWEEN IN lists LIKE patterns ESCAPE in LIKE IS NULL Boolean combinations Operator precedence EXISTS
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COUNT SUM AVG MIN and MAX GROUP BY HAVING Conditional aggregation Grouping expressions COUNT DISTINCT Aggregate NULL behavior
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SQL / Relational Foundations

NULLIF

Learn NULLIF in SQL through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Beginner

NULLIF is an atomic SQL topic inside Relational Foundations. This lesson focuses on how the NULLIF construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for NULLIF, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.

Topic-specific example

sql-01-10-nullif.sql
sql Try It Live 
SELECT revenue / NULLIF(visits, 0) AS revenue_per_visit FROM metrics;
Edge case / engineering note

For NULLIF, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

NULLIF Mastery Check →
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WHERE predicates