SELECT*FROMemp;DESCemp;SELECTempno,ename,sal,jobFROMemp;SELECTjobFROMemp;SELECTDISTINCTjobFROMemp;SELECTempnoASid,enameASname,sal*12"AnnualSalary"FROMemp;SELECTempnoASid,enameAS"Name",sal*12"AnnualSalary"FROMemp;SELECTename||'的职位是'||jobFROMemp;SELECTename||'的职位是'||job"Employee"FROMemp;--查询语句中使用连接表达式SELECTename,sal,comm,sal+commFROMemp;SELECTename,sal,comm,sal+nvl(comm,0)FROMemp;--NVL函数处理NULL值，comm为奖金项，有NULL值，用0代替SELECTename||'-'||comm||'-'||salASemployeeFROMemp;SELECTename,hiredateFROMemp;SELECTename,TO_CHAR(hiredate,'YYYY-MM-DD')hiredateFROMemp;SELECTename,sal,commFROMempWHEREsal<2000;SELECTename,sal,jobFROMempWHEREjob='SALESMAN';SELECTename,sal,hiredateFROMempWHEREhiredate>'01-1月-82';SELECTename,sal,hiredateFROMempWHEREhiredate>to_date('1982-1-1','YYYY-MM-DD');--日期类型数据的比较，SELECTename,salFROMempWHEREsalBETWEEN1500AND3000;SELECTename,jobFROMempWHEREjobIN('MANAGER','CLERK');SELECTename,jobFROMempWHEREenameLIKE'_A%';--%表示0到多个字符，_标识单个字符INSERTINTOemp(empno,ename)VALUES(5566,'JHON_SMITH');SELECTenameFROMempWHEREempno=5566;SELECTenameFROMempWHEREenameLIKE'%\_%'ESCAPE'\';SELECTenameFROMempWHEREenameLIKE'%U_%'ESCAPE'U';SELECTename,sal,commFROMempWHEREcommISNULL;SELECTename,sal,commFROMempWHEREcomm=NULL;--无返回结果SELECTename,sal,jobFROMempWHEREsal>1000ANDjob='CLERK';SELECTename,sal,jobFROMempWHEREsal>1000ORjob='CLERK';SELECTename,sal,commFROMempWHEREcommISNOTNULL;SELECTename,sal,jobFROMempWHEREjob='SALESMAN'ORjob='ANALYST'ANDsal>2000;--运算符的优先级规则：比较操作符>NOT>AND>ORSELECTename,salFROMempORDERBYsal;--默认为升序SELECTename,commFROMempORDERBYcomm;--在排序时，NULL值是最大的！SELECTename,salFROMempORDERBYsalDESC;--降序排列SELECTempno,ename,mgrFROMempWHEREdeptno=10ORDERBYmgrDESC;--有NULL值存在是，此列排在最前面SELECTenameFROMempORDERBYsalDESC;SELECTename,sal,sal*12FROMempORDERBYsal*12DESC;SELECTename,sal,sal*12annual_salaryFROMempORDERBYannual_salaryDESC;SELECTdeptno,dnameFROMdeptUNIONSELECTempno,enameFROMempORDERBY1;SELECTename,deptno,salFROMempORDERBYdeptnoASC,salDESC;分组查询：