数据库开发及ADO.NET(17)——去掉数据重复

1、执行如下的SQL语句，Alter和Insert单独执行。

ALTER TABLE T_Employee ADD FSubCompany VARCHAR(20);ALTER TABLE T_Employee ADD FDepartment VARCHAR(20);UPDATE T_Employee SET FSubCompany='Beijing',FDepartment='Development' 
WHERE FNumber='DEV001';UPDATE T_Employee SET FSubCompany='ShenZhen',FDepartment='Development' 
WHERE FNumber='DEV002';UPDATE T_Employee SET FSubCompany='Beijing',FDepartment='HumanResource' 
WHERE FNumber='HR001';UPDATE T_Employee SET FSubCompany='Beijing',FDepartment='HumanResource' 
WHERE FNumber='HR002';UPDATE T_Employee SET FSubCompany='Beijing',FDepartment='InfoTech' 
WHERE FNumber='IT001';UPDATE T_Employee SET FSubCompany='ShenZhen',FDepartment='InfoTech' 
WHERE FNumber='IT002';UPDATE T_Employee SET FSubCompany='Beijing',FDepartment='Sales' 
WHERE FNumber='SALES001';UPDATE T_Employee SET FSubCompany='Beijing',FDepartment='Sales'  
WHERE FNumber='SALES002';UPDATE T_Employee SET FSubCompany='ShenZhen',FDepartment='Sales'  
WHERE FNumber='SALES003';

（1）SELECT  FDepartment  FROM  T_Employee

（2）SELECT  DISTINCT  FDepartment  FROM  T_Employee

2、DISTINCT是对整个结果集进行数据重复处理的，而不是针对每一个列，因此下面的语句并不会只保留Fdepartment进行重复值处理：    

SELECT DISTINCT FDepartment,FSubCompany      FROM T_Employee