Explain PL/SQL IF and CASE control structures

IF...ELSIF...ELSE branches on one or more boolean conditions, evaluated top to bottom until one is true. CASE comes in two forms: a simple CASE compares one expression against several possible values, while a searched CASE evaluates independent boolean conditions — both can be used as a statement (CASE...END CASE) or, more commonly, as an expression that returns a value.

DECLARE
  v_salary NUMBER := 5500;
  v_grade  VARCHAR2(10);
BEGIN
  v_grade := CASE
    WHEN v_salary >= 10000 THEN 'A'
    WHEN v_salary >= 5000  THEN 'B'
    ELSE 'C'
  END;

  IF v_grade = 'A' THEN
    DBMS_OUTPUT.PUT_LINE('Top grade');
  ELSIF v_grade = 'B' THEN
    DBMS_OUTPUT.PUT_LINE('Mid grade');
  ELSE
    DBMS_OUTPUT.PUT_LINE('Entry grade');
  END IF;
END;
/