Why SQL's 'Second Highest Salary' Query Is a Classic Data Analysis Trap

A common SQL interview question — finding the second highest salary — appears simple but hides several real-world pitfalls that trip up even experienced developers. Rushing to write code without clarifying requirements can produce wrong results, such as returning duplicate salary values instead of the second unique pay tier. Three specific problems arise: salary ties, ambiguous employee definitions, and edge cases where too few records exist to return a valid result. The correct approach uses DENSE_RANK(), a window function that assigns shared ranks to tied values and sequences remaining tiers without gaps. Structuring the final query with Common Table Expressions (CTEs) further improves readability and maintainability over nested subqueries.