Sql增加字段(有些只能在ORACLE中运行)

[sql] 
增加字段  
alter table table_name add column_name varchar(200)  
  
  
删除字段  
ALTER TABLE table_NAME DROP COLUMN column_NAME  
  
  
修改字段类型  
ALTER TABLE table_name ALTER COLUMN column_name new_data_type  
  
  
修改表字段的长度(修改表结构)  
 alter table table_name modify column_name varchar(40) ;  
  
  
改名  
  
sp_rename  

sp_rename [ @objname = ] 'object_name' ,  
  
  
    [ @newname = ] 'new_name'  
  
  
    [ , [ @objtype = ] 'object_type' ]  
  
  
--假设要处理的表名为: tb  
  
  
--判断要添加列的表中是否有主键  
  
  
if exists(select 1 from sysobjects where parent_obj=object_id('tb') and xtype='PK')  
  
  
begin  
  
  
print '表中已经有主键,列只能做为普通列添加'  
  
  
--添加int类型的列,默认值为0  
  
  
alter table tb add 列名 int default 0  
  
  
end  
  
  
else  
  
  
begin  
  
  
print '表中无主键,添加主键列'  
  
  
 查询表中的某些字段重复记录  
         select count(*),column_name from table_name group by column_name having count(*)>1;  
  
  
查询并修改数据(如将67001改为68701,67101改为68801)  
        select code,('68' || (substr(code, 2, 1) + substr(code,3,1)) || substr(code,4,2)) as code2 from table_name where code like '67___' ;  
        update table_name set code = ('68' || (substr(code, 2, 1) + substr(code,3,1)) || substr(code,4,2)), parentid='68'  where code like '67___' ;