在将某一约束应用于泛型类型参数时，必须存在从具体参数到该约束类型的隐式标识或引用转换。
When a constraint is applied to a generic type parameter, an implicit identity or reference conversion must exist from the concrete argument to the type of the constraint.
这些支持通过行标识符(RID_BIT或RID)内置函数、ROW CHANGE TOKEN表达式、基于时间的更新检测和隐式隐藏的列实现。
This support is added using the row identifier (RID_BIT or RID) built-in function, the row CHANGE TOKEN expression, the time-based update detection, and implicitly hidden columns.
如果您拥有类，则可移除约束或执行某一操作以启用隐式引用或标识转换。
If you own the class, you can remove the constraint or else do something to enable an implicit reference or identity conversion.
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