SQL CASE WHEN Quant Interview Guide
SQL CASE WHEN quant interview guide for conditional flags, buckets, conditional aggregation, null handling, examples, and readability.
Candidates building conditional flags, buckets, and metrics.
CASE creates conditional values
CASE WHEN lets a query assign labels, flags, or values based on conditions. It is useful for buckets and conditional metrics.
Conditional aggregation is common
SUM or AVG over CASE expressions can count or measure rows matching a condition. Be explicit about ELSE zero versus ELSE null.
Concrete example
To compute buy volume and sell volume in one query, sum quantity inside separate CASE expressions based on trade side and null behavior.
Keep business logic readable
Nested CASE statements can become hard to audit. Use CTEs or named intermediate flags when the logic has multiple steps.
Common mistakes
Candidates often forget ELSE behavior. In SQL, missing ELSE can produce null, which changes sums, averages, and downstream filters.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.