Oracle用户操作的学习笔记（一）

1.查询用户下的所有对象(表，过程，自增序列等)

select object_name,object_type from user_objects order by object_name,object_type;

2.oracle取值函数
round(数值，小数点位数)：四舍五入

select round(((salary*12)/365),2) "Daily day" from employees;

trunc(): 去尾法

select trunc((salary*12)/365) "Daily day" from employees;

3.字符格式函数
upper(""):大写
lower(""):小写
initcap(""):首字母大写
4.时间格式转换

select to_char(sysdate,'FMMonth DD YYYY') from dual;

5.数字字符串转number类型

select to_number('4564646')+1 from dual;

6.null值标识转换
nvl():

select nvl(to_char(null),'no value') from dual;

nvl2():

select nvl2(null,'not null','no value') from dual;

7.case的用法
带参数

SELECT UNIQUE COUNTRY_ID ID,
       CASE COUNTRY_ID
         WHEN 'AU' THEN 'Australia'
         WHEN 'BR' THEN 'Brazil'
         WHEN 'CA' THEN 'Canada'
         WHEN 'CH' THEN 'Switzerland'
         WHEN 'CN' THEN 'China'
         WHEN 'DE' THEN 'Germany'
         WHEN 'IN' THEN 'India'
         WHEN 'IT' THEN 'Italy'
         WHEN 'JP' THEN 'Japan'
         WHEN 'MX' THEN 'Mexico'
         WHEN 'NL' THEN 'Netherlands'
         WHEN 'SG' THEN 'Singapore'
         WHEN 'UK' THEN 'United Kingdom'
         WHEN 'US' THEN 'United States'
       ELSE 'Unknown'
       END COUNTRY
FROM LOCATIONS
ORDER BY COUNTRY_ID;

不带参数

SELECT LAST_NAME "Name",
HIRE_DATE "Started",
SALARY "Salary",
CASE
  WHEN HIRE_DATE < TO_DATE('01-Jan-03', 'dd-mon-yy')
    THEN TRUNC(SALARY*1.15, 0)
  WHEN HIRE_DATE >= TO_DATE('01-Jan-03', 'dd-mon-yy') AND
       HIRE_DATE < TO_DATE('01-Jan-06', 'dd-mon-yy')
    THEN TRUNC(SALARY*1.10, 0)
  WHEN HIRE_DATE >= TO_DATE('01-Jan-06', 'dd-mon-yy') AND
       HIRE_DATE < TO_DATE('01-Jan-07', 'dd-mon-yy')
    THEN TRUNC(SALARY*1.05, 0)
  ELSE SALARY
END "Proposed Salary"
FROM EMPLOYEES
WHERE DEPARTMENT_ID = 100
ORDER BY HIRE_DATE;

8.DECODE关键使用

SELECT LAST_NAME, JOB_ID, SALARY,
DECODE(JOB_ID,
  'PU_CLERK', SALARY * 1.10,
  'SH_CLERK', SALARY * 1.15,
  'ST_CLERK', SALARY * 1.20,
  SALARY) "Proposed Salary"
FROM EMPLOYEES
WHERE JOB_ID LIKE '%_CLERK'
AND LAST_NAME < 'E'
ORDER BY LAST_NAME;