The microsoft jet odbc driver always returns unique index and primary key columns as nullable regardless of whether they are nullable or not Microsoft jet odbc驱动程序总是将唯一的索引和主键列返回为可以为空,而不管它们是否可以为空。
Because of the ability to have multiuser access to the primary key columns , it is important that the primary key column values not be changed during synchronizations 由于可以让多个用户访问主键列,因此在同步期间不更改主键列值是很重要的。
For example , if a tableadapter is configured to query data from a table that does not have a primary key column defined , it does not generate dbdirect methods 例如,如果将tableadapter配置为从未定义主键列的表中查询数据,它将不会生成dbdirect方法。
Requires extra processing at the data source to determine primary key column information . this additional processing can hinder performance 当使用fillschema或将missingschemaaction设置为addwithkey时,将需要在数据源中进行额外的处理来确定主键列信息。
If informational check constraints exist on the primary key column , you should explicitly specify informational check constraints on their corresponding foreign key columns 如果在主键列上存在信息检查约束,那么应该在它们相应的外键列上指定信息检查约束。
In a distributed environment it is essential to ensure that the same value is not inserted into a primary key column or any other unique column at more than one node 在分布式环境中,确保没有将同一值插入到多个节点上的主键列或任何其他唯一列,这一点很重要。
If no primary key columns are returned but unique columns are , the unique columns are used as the primary key if , and only if , all of the unique columns are nonnullable 如果未返回主键列,但返回了唯一列,则当且仅当所有唯一列都不可为空时,将唯一列用作主键。
If no primary key columns are returned but unique columns are , the unique columns are used as the primary key if , and only if , all the unique columns are nonnullable 如果未返回任何主键列,但返回了唯一列,则当且仅当所有唯一列都不可为空时,唯一列才用作主键。