Oracle PL/SQL: CASE Expression vs. CASE Statement

The CASE expression and CASE statement are two conditional control structures in Oracle PL/SQL, each serving distinct purposes. The CASE expression evaluates conditional logic and returns a single scalar value, while the CASE statement evaluates the same logic to execute procedural actions or statements.

A CASE statement can serve as the primary execution control path within a PL/SQL block, handling multiple statements based on the conditions. Conversely, CASE expressions are limited to returning a single value and are often used inside SQL or PL/SQL assignments.

In syntax, CASE statements are terminated with the END CASE; keyword, whereas CASE expressions conclude with END.

The examples provided illustrate how both structures can be employed. A CASE expression returns a value based on the job_id variable, assigning specific bonuses to different job types. On the other hand, a CASE statement executes different block of statements based on the job_id, outputting the respective department name for each type of job.

A critical detail is the handling of unmatched cases. In a CASE statement, if no WHEN clause conditions match and there's no default ELSE clause, Oracle raises a runtime exception, ORA-06592: CASE not found. Meanwhile, a CASE expression, lacking a matching condition and no ELSE clause, simply evaluates to NULL, without throwing an error.