For this explanation, assume that a searched CASE expression has this syntax:

CASE
WHEN boolean_expression_1 THEN result_1
WHEN boolean_expression_2 THEN result_2
...
WHEN boolean_expression_n THEN result_n
[ ELSE
  else_result ]
END]

2.1 Searched CASE Expression

This example assigns the value of a searched CASE expression to the variable appraisal.

DECLARE
  grade      CHAR(1) := 'B';
  appraisal  VARCHAR2(120);
  id         NUMBER  := 8429862;
  attendance NUMBER := 150;
  min_days   CONSTANT NUMBER := 200;
  
  FUNCTION attends_this_school (id NUMBER)
    RETURN BOOLEAN IS
  BEGIN
    RETURN TRUE;
  END;
BEGIN
  appraisal :=
  CASE
    WHEN attends_this_school(id) = FALSE
      THEN 'Student not enrolled'
    WHEN grade = 'F' OR attendance < min_days
      THEN 'Poor (poor performance or bad attendance)'
    WHEN grade = 'A' THEN 'Excellent'
    WHEN grade = 'B' THEN 'Very Good'
    WHEN grade = 'C' THEN 'Good'
    WHEN grade = 'D' THEN 'Fair'
    ELSE 'No such grade'
  END;
  DBMS_OUTPUT.PUT_LINE
    ('Result for student ' || id || ' is ' || appraisal);
END;
/
-- run result 
Result for student 8429862 is Poor (poor performance or bad attendance)
 

2.2 Searched CASE Expression with WHEN … IS NULL

This example uses a searched CASE expression

DECLARE
  grade CHAR(1); -- NULL by default
  appraisal VARCHAR2(20);
BEGIN
  appraisal :=
    CASE
      WHEN grade IS NULL THEN 'No grade assigned'
      WHEN grade = 'A' THEN 'Excellent'
      WHEN grade = 'B' THEN 'Very Good'
      WHEN grade = 'C' THEN 'Good'
      WHEN grade = 'D' THEN 'Fair'
      WHEN grade = 'F' THEN 'Poor'
      ELSE 'No such grade'
    END;
    DBMS_OUTPUT.PUT_LINE ('Grade ' || grade || ' is ' || appraisal);
END;
/
-- run result 
Grade  is No grade assigned

PL/SQL procedure successfully completed.