Which SQL construct will evaluate a condition and return a value when that condition is met, such as mapping a state to a region?

• A. CASE
• B. WHERE
• C. THEN
• D. END

Answer: (A)

CASE expressions evaluate conditions and return a value when a condition matches. This lets you map inputs to outputs directly in a query, such as turning a state into a region. For example, you can write a CASE expression in the SELECT list that checks the state and returns "West" for California, Oregon, and Washington, "Northeast" for New York and nearby states, and an "Other" category otherwise. The CASE scans each WHEN in order and returns the first matching THEN value; if none match, the ELSE value is used.

This is different from filtering rows, which is what a WHERE clause does—it decides which rows to include in the result set rather than producing a value for each row. THEN and END are part of the CASE syntax: THEN specifies the value to return for a matching condition, and END ends the CASE expression. So the CASE construct is the tool that evaluates conditions and produces a value per row, enabling the state-to-region mapping.