数据库中通用函数和条件表达式有哪些

SELECT SALARY, NVL(TO_CHAR(COMMISSioN_PCT), 0) FROM EMPLOYEES;

SELECT LAST_NAME,

       SALARY,

       COMMISSION_PCT,

       NVL2(COMMISSION_PCT, 'SAL+COMM', 'SAL') INCOME

  FROM EMPLOYEES

 WHERE DEPARTMENT_ID IN (50, 80);

SELECT FIRST_NAME,

       LENGTH(FIRST_NAME) "expr1",

       LAST_NAME,

       LENGTH(LAST_NAME) "expr2",

       NULLIF(LENGTH(FIRST_NAME), LENGTH(LAST_NAME)) RESULT

  FROM EMPLOYEES;

SELECT COALESCE(NULL, 1, 2, 3, 4) FROM DUAL;

SELECT COALESCE(NULL, NULL, 2, 3, 4) FROM DUAL;

SELECT last_name,salary,

       (CASE WHEN salary<5000 THEN 'Low'

             WHEN salary<10000 THEN 'Medium'

             WHEN salary<20000 THEN 'Good'

             ELSE 'excellent'

       END) qualified_salary

FROM employees;

SELECT PRODUCT_ID,

       DECODE(WAREHOUSE_ID,

              1, 'Southlake',

              2, 'San Francisco',

              3, 'New Jersey',

              4, 'Seattle',

              'Non-domestic') "Location of inventory" 　　　

  FROM INVENTORIES 　　　

 WHERE PRODUCT_ID < 1775;