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
先group by 后 order by SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ] * | expression [ AS output_name ] [, ...] [ FROM from_item [, ...] ] [ WHERE condition ] [ GROUP BY expression [, ...] ] [ HAVING condition [, ...] ] [ {