46. 日期函数
months_between(): 求出给定日期范围的月数
add_months(): 在指定的日期上加上指定的月数, 求出之后的日期
next_day(): 指定日期的下一个日期
last_day(): 求出给定日期当月的最后一天日期
47.
select empno, ename, months_between(sysdate, hiredate) from emp;
select empno, ename, round(months_between(sysdate, hiredate)) from emp;
48. select sysdate, add_months(sysdate, 4) from dual;
49. select next_day(sysdate, '星期一') from dual;
50. select last_day(sysdate) from dual;
51. 转换函数
to_char(): 转换成字符串
to_number(): 转换成数字
to_date(): 转换成日期
52. 查询所有雇员的雇员编号, 姓名, 雇佣日期
select empno,
ename,
to_char(hiredate, 'yyyy') year,
to_char(hiredate, 'mm') months,
to_char(hiredate, 'dd') day
from emp;
select empno, ename, to_char(hiredate, 'yyyy-mm-dd') from emp;
select empno, ename, to_char(hiredate, 'fmyyyy-mm-dd') from emp;
53. 查询所有雇员的编号, 姓名和工资
select empno, ename, sal from emp;
select empno, ename, to_char(sal, '99,999') from emp;
select empno, ename, to_char(sal, 'L99,999') from emp;
select empno, ename, to_char(sal, '$99,999') from emp;
54. select to_number('123') + to_number('123') from dual;
55. 将一个字符串转换成日期类型
select to_date('2009-01-01', 'yyyy-mm-dd') from dual;
56. 求出每个雇员的年薪(要求加上奖金)
select empno, ename, sal, comm, (sal + comm) * 12 from emp;
select empno, ename, sal, comm, nvl(comm, 0), (sal + nvl(comm, 0)) * 12 income from emp;
57. decode() 函数类似于 if....elsif...else 语句
select decode(1, 1, '内容是 1', 2, '内容是 2', 3, '内容是 3') from dual;
58. 查询出雇员的编号, 姓名, 雇佣日期及工作, 要求将雇员的工作替换成以下信息:
select empno 雇员编号,
ename 雇员姓名,
hiredate 雇佣日期,
'CLERK', '业务员',
'SALESMAN', '销售人员',
'MANAGER', '经理',
'ANALYST', '分析员',
'PRESIDENT', '总裁'
) 职位
from emp;
59. 笛卡尔积(交差连接)
select * from emp, dept;
select * from emp cross join dept;
60. 内连接
select * from emp e, dept d where e.deptno = d.deptno;
select * from emp e inner join dept d on e.deptno = d.deptno;
select * from emp e join dept d on e.deptno = d.deptno;
61. 自然连接
select * from emp natural join dept;
select * from emp e join dept d using(deptno);
62. 要求查询出雇员的编号, 姓名, 部门的编号, 名称, 地址
select e.empno, e.ename, d.deptno, d.dname, d.loc from emp e, dept d where e.deptno = d.deptno;
63. 要求查询出雇员的姓名, 工作, 雇员的直接上级领导姓名
select e.ename, e.job, m.ename from emp e, emp m where e.mgr = m.empno;
64. 要求查询出雇员的姓名, 工作, 雇员的直接上级领导姓名以及部门名称
select e.ename, e.job, m.ename, d.dname from emp e, emp m, dept d where e.mgr = m.empno and e.deptno = d.deptno;
65. 要求查询出每个雇员的姓名, 工资, 部门名称, 工资在公司的等级(salgrade), 及其领导的姓名及工资所在公司的等级
select e.ename, e.sal, d.dname, s.grade, m.ename, m.sal, ms.grade
from emp e, dept d, salgrade s, emp m, salgrade ms
where e.deptno = d.deptno
and e.sal between s.losal and s.hisal
and e.mgr = m.empno
and m.sal between ms.losal and ms.hisal;
select e.ename,
e.sal,
d.dname,
decode(s.grade, 1, '第五等级', 2, '第四等级', 3, '第三等级', 4, '第二等级', 5, '第一等级'),
m.ename,
m.sal,
decode(ms.grade, 1, '第五等级', 2, '第四等级', 3, '第三等级', 4, '第二等级', 5, '第一等级')
from emp e, dept d, salgrade s, emp m, salgrade ms
where e.deptno = d.deptno and e.sal between s.losal and s.hisal and e.mgr = m.empno
and m.sal between ms.losal and ms.hisal;
66. select empno, ename, d.deptno, dname, loc from emp e, dept d where e.deptno = d.deptno;
select empno, ename, d.deptno, dname, loc from emp e inner join dept d on e.deptno = d.deptno;
67. 左外连接
select empno, ename, d.deptno, dname, loc from emp e, dept d where e.deptno = d.deptno(+);
select empno, ename, d.deptno, dname, loc from emp e left outer join dept d on e.deptno = d.deptno;
select empno, ename, d.deptno, dname, loc from emp e left join dept d on e.de