case表达式详解

CASE 表达式

---------格式一---------
CASE 条件表达式
  WHEN 条件表达式结果1 THEN 
     语句段1
  WHEN 条件表达式结果2 THEN
     语句段2
  ......
  WHEN 条件表达式结果n THEN
     语句段n
  [ELSE 条件表达式结果]
END;
---------格式二---------
CASE 
  WHEN 条件表达式1 THEN
     语句段1
  WHEN 条件表达式2 THEN
     语句段2
  ......
  WHEN 条件表达式n THEN 
     语句段n
  [ELSE 语句段]
END;

例4:

DECLARE
  V_grade char(1) := UPPER('&p_grade');
  V_appraisal VARCHAR2(20);
BEGIN
  V_appraisal :=
  CASE v_grade
    WHEN 'A' THEN 'Excellent'
    WHEN 'B' THEN 'Very Good'
    WHEN 'C' THEN 'Good'
    ELSE 'No such grade'
  END;
  DBMS_OUTPUT.PUT_LINE('Grade:'||v_grade||'  Appraisal: '|| v_appraisal);
END;

例5:

DECLARE
   v_first_name employees.first_name%TYPE;
   v_job_id employees.job_id%TYPE;
   v_salary employees.salary%TYPE;
   v_sal_raise NUMBER(3,2);
BEGIN
   SELECT first_name,   job_id,   salary INTO
          v_first_name, v_job_id, v_salary
   FROM employees WHERE employee_id = &emp_id;
   CASE
      WHEN v_job_id = 'PU_CLERK' THEN
         IF v_salary < 3000 THEN v_sal_raise := .08;
         ELSE v_sal_raise := .07;
         END IF;
      WHEN v_job_id = 'SH_CLERK' THEN
         IF v_salary < 4000 THEN v_sal_raise := .06;
         ELSE v_sal_raise := .05;
         END IF;
      WHEN v_job_id = 'ST_CLERK' THEN
         IF v_salary < 3500 THEN v_sal_raise := .04;
         ELSE v_sal_raise := .03;
         END IF;
      ELSE
         DBMS_OUTPUT.PUT_LINE('该岗位不涨工资: '||v_job_id);
   END CASE;
   DBMS_OUTPUT.PUT_LINE(v_first_name||'的岗位是'||v_job_id
                                    ||'、的工资是'||v_salary
                                    ||'、工资涨幅是'||v_sal_raise);
END;