本文深入探讨了数据库设计中的常见问题，如过多的表格和重复的数据字段，并提出了解决这些问题的方法。特别关注了电子邮件、邮政编码等常用字段的类型和长度选择，以及在MySQL中实现自定义数据类型的挑战。通过研究SQL Server、Oracle等平台的功能，文章指出MySQL在这方面存在限制，并提供了替代策略。
As you know,we always design database again and again. There are too much tables in these databases.
And also there are too many data fields are same ,like zip code,telephone,email,md5,loginid,password,create time ... etc
I always think how to design these field's data type and length.always,even i defined some rule before.
So, I want some function can help me add some new data type like email(varchar (20)),zip code (varchar 6). Bla bla bla.
I had do some research :"Sql server" and "Oracle" can do this like 'create type ...' or 'sp_addtype' .But there is no way for MySql.
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