英语翻译9.Although primary keys are notactually required,most da
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英语翻译
9.
Although primary keys are notactually required,most database designers en sure that every table they create has a primary key so that future datamanipulation is possible and manageable.Any column in a table can be established as the primary key,as long asit meets the following conditions:Notwo rows can have the same primary key value.Every row must have a primary key value (primary key columns may notallow NULL values).Values in primarykey columns can never be modified or updated.our ATM card at a cash machine,you are using databases for PIN number verification and balance checking.
9.
Although primary keys are notactually required,most database designers en sure that every table they create has a primary key so that future datamanipulation is possible and manageable.Any column in a table can be established as the primary key,as long asit meets the following conditions:Notwo rows can have the same primary key value.Every row must have a primary key value (primary key columns may notallow NULL values).Values in primarykey columns can never be modified or updated.our ATM card at a cash machine,you are using databases for PIN number verification and balance checking.
虽然主键其实不是必须的,但多数的数据库设计者都会确保他们创建的每个表格都有主键,这样能让将来的数据操作变得可能和可控.表格中的任何列都可以作为主键,只要它满足下列条件:
- 任何两行数据都不能含有相同的主键值.
- 每一行都必须有主键值(主键列不允许空值).
-主键列的值永远不能被改变或更新.
提款机上使用的ATM卡,你要使用数据库来验证PIN数值和查询账户余额.
- 任何两行数据都不能含有相同的主键值.
- 每一行都必须有主键值(主键列不允许空值).
-主键列的值永远不能被改变或更新.
提款机上使用的ATM卡,你要使用数据库来验证PIN数值和查询账户余额.
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