组函数AVGCOUNTMAXMINSUMVARIANCE:方差STDDEV:标准差 SELECT AVG(salary), MAX(salary), MIN(salary), SUM(salary)FROM employees WHERE job_id LIKE '%REP%'; SELECT MIN(hire_date), MAX(hire_date) FROM employees; COUNT(expr) 返回expr为非空值的行数:SELECT COUNT(commission_pct) …

大小写转换函数LOWER('SQL Course') = sql courseUPPER('SQL Course') = SQL COURSEINITCAP('SQL Course') = Sql CourseSELECT employee_id, last_name, department_idFROM employeesWHERE last_name = 'higgins'; SELECT employee_id, last_name, department_idFROM employees…

隐式转换select * from emp where empno='7788'字符(char,varchar2)转换为数字(number)或日期(date)数字或日期转换为字符 显式转换字符转换为数字或日期(TO_NUMBER, TO_DATE)数字或日期转换为字符(TO_CHAR) TO_CHAR(date, 'format_model')select sysdate, to_char(sysdate,'yyyy') yyyy, to_char(sysdate,'year') year,fr…

Oracle数据库  内置系统函数主要分为以下类别:数学函数.字符串函数.日期函数.转换函数.聚合函数.分析聚合函数 一.数学函数 ------------返回数字       abs(n):返回数字n的绝对值      ceil(n):返回>=数字n的最小整数      floor(n):返回<=数字n的最大整数      round(n,[m]):做四舍五入运算,如果m缺省则四舍五入到整数位                               m<0,四舍五入到小数点的前m位…

使用子查询简单子查询SELECT select_listFROM tableWHERE expr operator (SELECT select_list FROM table);子查询可以出现在select,from和where之后,都是可以的.SELECT last_name, salaryFROM employeesWHERE salary > (SELECT salary FROM employees WHERE last_name = 'Abel'); SELECT last_name…

常用组函数: 1.ccount() 求出全部记录数. 2.max() 求出一组最大值 3.min() 求出一组最小值 4.avg() 求出平均值 5.sum() 求和 --1.统计员工数量: select count(empno) from emp; --2.求出最高薪资 select max(sal) from emp; --3.求出最低薪资 select min(sal) from emp; --4.求出平均薪资 select avg(sal) from emp; --查询各部门员工数量 s…

重建scott用户@?/rdbms/admin/utlsampl.sql@--执行?--$ORACLE_HOME 字符区分大小写:SELECT last_name, job_id, department_idFROM employeesWHERE last_name = 'Whalen' ; 使用字符函数:SELECT last_name, job_id, department_idFROM employeesWHERE upper(last_name) = 'WHALEN' ; SELECT…

使用连接SQL 1999SELECT table1.column, table2.columnFROM table1[NATURAL JOIN table2] |[JOIN table2 USING (column_name)] |[JOIN table2 ON (table1.column_name = table2.column_name)]|[LEFT|RIGHT|FULL OUTER JOIN table2 ON (table1.column_name = table2.column_n…

使用INSERT语句INSERT INTO table [(column [, column...])]VALUES (value [, value...]); INSERT INTO departments(department_id, department_name, manager_id, location_id)VALUES (70, 'Public Relations', 100, 1700);字符和日期需要用单引号 INSERT INTO employeesVALUES (114,…

第一节课: 启动数据库并且使用特定用户连接:su - oracle; 启动sqlplus并且使用sys连接:conn / as sysdba; 启动数据库:startup; 解锁用户:alter user hr identified by hr;alter user hr account unlock; 使用hr连接:conn hr/hr;select * from tab;desc employees;select * from departments; 开发工具:plsql develope…