摘要： 组函数AVGCOUNTMAXMINSUMVARIANCE：方差STDDEV：标准差SELECT AVG(salary), MAX(salary),MIN(salary), SUM(salary)FROM employeesWHERE 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)FROM employeesWHERE department_id = 80;select cou 阅读全文

摘要： 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,from dual;select sysda 阅读全文

摘要： 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 employeesWHERE LOWER(last_na 阅读全文

摘要： 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 last_name, job_id, department_idFROM 阅读全文

摘要： 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 developer;toad特殊字符：SELECT department_name || q'[ Department& 阅读全文