Where can a CASE appear in a query?

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Accepted Answer

CASE is an expression in SQL - it evaluates to a single value just like a column reference or function call. Because it produces a value, you can embed it anywhere an expression is valid: SELECT lists, WHERE predicates, HAVING clauses, ORDER BY, and even CHECK constraints. Programmers coming from procedural languages often confuse it with a switch statement, but there are no code blocks or side effects - only a returned value.