oracle 的sql语句基础查询

select userenv('language') from dual;--AMERICAN_AMERICA.ZHS16GBKselect * from V$NLS_PARAMETERS--AMERICAN--===========解锁scott用户并重新设置密码alter user scott account unlock;alter user scott identified by tiger;
--===============================================================基本查询--1.查询出所有emp中的信息，并用中文进行字段重命名select empno as "员工编号",ename "员工姓名",job 职位,mgr "领导编号",hiredate "入职日期",sal "工资",comm "奖金",deptno "部门编号" from emp;

--2.查询emp表中员工的job信息，并去除重复信息select distinct(job) from emp;

--3.查询emp表中员工的全年的工资总和(sal总和)select ename,12*sal from emp;
--4.查询emp表中员工的全年收入总和(sal+comm的总和)select ename,12*sal+nvl(comm,0) from emp;
--5.查询emp表中员工编号，姓名--输出格式如下：编号:xxx，姓名：xxx----Concat拼接方式select concat(concat('编号:',empno),concat('，姓名：',ename)) from emp;
----Oracle的||方式select '编号'||empno||'，姓名：'||ename from emp;
--=============================================条件查询--1.查询工资大于1500的员工select * from emp where sal >= 1500;
--2.查询工资大于1500并且有奖金的雇员select * from emp where sal >= 1500 and comm  is not null;
--3.查询工资大于1500或者有奖金的雇员select * from emp where sal >= 1500 or comm  is not null;
--4.查询工资大于1500并且没有奖金的雇员select * from emp where sal >= 1500 and comm  is null;
--5.查询员工姓名为smith的员工select * from emp where ename = 'SMITH';
--=============================================范围查询--1.查询工资大于1500但小于3000的全部雇员---->=,<=方式select * from emp where sal >= 1500 and sal <= 3000;
----between and方式select * from emp where sal between 1500 and 3000;
--2.查询1981-1-1到1981-12-31号入职的雇员（between and）select * from emp where hiredate between to_date('1981-1-1','yyyy-MM-dd') and to_date('1981-12-31','yyyy-MM-dd')
--3.查询员工编号是7369,7654,7566的员工----OR方式select * from emp where empno = 7369 or empno = 7654 or empno = 7566----IN方式select * from emp where empno in(7369,7654,7566)
--4.查询雇员姓名是'SMITH','ALLEN','WARD'的雇员信息----IN方式select * from emp where ename in('SMITH','ALLEN','WARD')--=============================================模糊查询like--1.查询所有雇员姓名中第二个字符有‘M’的雇员select * from emp where ename like '_M%'
--2.查询名字中带有‘M’的雇员select * from emp where ename like '%M%'
--3.查询雇员编号不是7369的雇员信息----<>方式select * from emp where empno <> 7369;----!=方式select * from emp where empno != 7369;--=============================================排序 order by--1.查询雇员的工资进行降序排序select ename,sal from emp order by sal desc;
--2.查询雇员的奖金并做降序排序（关于nulls first/nulls last）select ename,comm from emp order by comm desc nulls last;
--3.查询雇员的工资做降序排列并且其中奖金部分是升序排序select ename,
4000
sal,comm from emp order by sal desc,comm asc;
--===========单行函数/*伪表，虚表：dual  没有任何的实际意义，只是为了补全Oracle查询语法*/--字符函数--1.将'smith'转换成大写--关键字:upperselect upper('smith') from dual;
--2.将'SMITH'转换成小写--关键字:lowerselect lower(ename) from emp;
--3.将'smith'首字母大写--关键字:initcapselect initcap(ename) from emp;
--4.将'helloworld'截取字符串成'hello'--关键字substrselect substr('helloworld',0,5) from dual;
--5.获取'hello'的字符串长度--关键字lengthselect length('hello') from dual;
--6.将'hello'中的l用x进行替换--关键字replaceselect replace('hello','l','x') from dual;
--数值函数--1.将15.66进行四舍五入（从-2到2）--关键字roundselect round(15.66,-2) from dual;  --0select round(15.66,-1) from dual; --20select round(15.66,0) from dual; --16select round(15.66,1) from dual; --15.7select round(15.66,2) from dual; --15.66
--2.将15.66进行截断（从-2到2）--关键字truncselect trunc(15.66,-2) from dual;  --0select trunc(15.66,-1) from dual; --10select trunc(15.66,0) from dual; --15select trunc(15.66,1) from dual; --15.6select trunc(15.66,2) from dual; --15.66

--3.对15/3进行求余数--关键字modselect mod(15,3) from dual;
--日期函数--1.查询系统时间--关键字sysdateselect sysdate from dual;
--2.查询雇员进入公司的周数select ename,(sysdate-hiredate)/7 from emp
--3.查询雇员进入公司的月数--关键字months_betweenselect ename,months_between(sysdate,hiredate) from emp;
--4.求出三个月后的日期--关键字add_monthsselect ename,hiredate,add_months(hiredate,3) from emp;
--转换函数--1.将系统日期显示为yyyy-mm-dd hh:mi:ss(去掉补零和24小时显示时间)--关键字to_charselect to_char(sysdate,'yyyyfm-mm-dd hh24:mi:ss') from dual;
----显示成年月日select to_char(sysdate,'yyyy')||'年'||to_char(sysdate,'MM')||'月'||to_char(sysdate,'dd')||'日' from dual;--2.将字符串'1981-1-1'转换成日期类型--关键字to_dateselect to_date('1981-1-1','yyyy-MM-dd') from dual;
select to_number('99') from dual;select to_char(99) from dual;--通用函数--1.空值的处理函数select nvl(comm,0) from emp;--2.nvl2(判断值,空返回值,非空返回值)select nvl2('xxxxxx','1','2') from dual;
--条件表达式--1.查询员工的job内容并转成中文显示----decode方式select ename,decode(job,'CLERK','柜员','SALESMAN','销售','MANAGER','管理','其他') from emp;----case when then end方式select ename, case job when 'CLERK'  then  '柜员'                       when 'SALESMAN'  then  '销售'                       when 'MANAGER'  then  '管理'     else       '其他'       end from emp;         --===========多行函数--1.查询所有员工记录数--关键字countselect count(*) from emp;
--2.查询佣金的总数--（如何查询某个字段的总数量）select sum(comm) from emp;
--3.查询最低工资--关键字minselect min(sal) from emp;
--4.查询最高工资--关键字maxselect max(sal) from emp;
--5.查询平均工资--关键字avgselect avg(sal) from emp;
--6.查询20号部门的员工工资总和select sum(sal) from emp where deptno = 20;
--======================================分组函数--1.查询部门编号及人数--分组查询关键字group byselect deptno,count(*) from emp group by deptno;
--2.查询每个部门编号及平均工资select deptno,avg(sal) from emp group by deptno;
--3.查询部门名称，部门编号，平均工资select dname,emp.deptno,avg(sal) from dept,emp where dept.deptno = emp.deptno group by emp.deptno,dname
--4.查询出部门人数大于5人的部门select deptno,count(*) from emp group by deptno having count(*) > 5
--5.查询部门编号，部门名称，平均工资且平均工资大于2000select emp.deptno,dname,avg(sal) from emp,dept where emp.deptno = dept.deptnogroup by emp.deptno,dname having avg(sal) > 2000;