解决问题：字段类型为char的总是占用指定字节长度(末尾好多空白符号),varchar数据类型长度一个汉字占2个字节，内容存储为中文的字段个人建议全部使用nvarchar。
操作说明：打开SQL Server Management Studio，选中你要更新字段类型的数据库，点新建查询菜单，执行下面的语句即可。
详细代码：
--批量替换数据库中所有用户数据表中字段数据类型为char和varchar到nvarchar的脚本
declare @TableName nvarchar(255) --定义数据表名变量
declare @ColumnName nvarchar(255) --定义字段名处变量
declare @ConstraintName varchar (250)--定义当前查询的约束变量
declare @cllength nvarchar(8) --定义字段长度变量
declare @tyname nvarchar(255) --定义字段类型变量
declare @Sql nvarchar(2000) --定义循环执行SQL语句
declare mycursor1 cursor fast_forward for select a.name as tbname,b.name as clname, b.prec as cllength, c.name as tpname from sysobjects a inner join syscolumns b on b.id=a.id and a.type='U' inner join systypes c on b.xusertype=c.xusertype where a.xtype='U' and (c.name='char' or c.name='nchar') --定义一个游标对象
open mycursor1 --打开游标
fetch next from mycursor1 into @TableName,@ColumnName,@cllength,@tyname--取数据到临时变量
while @@fetch_status = 0 --系统@@fetch_status = 0 时循环结束
begin
--1删除指定数据表指定字段对应的所有约束
--声明读取数据表中指定字段对应的所有约束列表游标
declare mycursor2 cursor for select name from sysobjects left join sysconstraints on sysconstraints.constid=sysobjects.id where parent_obj=OBJECT_ID(''+@TableName+'') and colid=(select colid from syscolumns where id=OBJECT_ID(''+@TableName+'') and OBJECTPROPERTY(id, N'IsUserTable') = 1 and upper(name)=upper(@ColumnName))
--打开游标
open mycursor2
--从游标里取出数据赋值到主键约束名称变量中
fetch next from mycursor2 into @ConstraintName
--如果游标执行成功
while (@@fetch_status=0)
begin
--删除当前找到的约束
print '当前删除语句'+'ALTER TABLE ['+@TableName+'] DROP CONSTRAINT ['+@ConstraintName+']'
exec ('ALTER TABLE ['+@TableName+'] DROP CONSTRAINT ['+@ConstraintName+']')
--print '已成功删除数据表['+@TableName+']字段['+@ColumnName+']对应的约束['+@ConstraintName+']'
--用游标去取下一条记录
fetch next from mycursor2 into @ConstraintName
end
--关闭游标
close mycursor2
--撤销游标
deallocate mycursor2
--2循环执行更新字段语句
set @Sql = 'alter table ['+@TableName+'] alter column ['+ @ColumnName +'] nvarchar('+@cllength+');'--定义当前更新字段类型执行语句
execute(@Sql);
print '当更新语句'+@Sql
fetch next from mycursor1 into @TableName,@ColumnName,@cllength,@tyname --再次取值
end
close mycursor1 --关闭游标
deallocate mycursor1 --删除游标