r****s
发帖数: 12 | 1 keys are attributes or sets of attributes that uniquely identify an
object within its class or an entity within its entity set.no two
objects in a class may agree in their values for each of a set of
attributes that constitutes a key.
single-value constraints are requirements that the value in a certain
role be unique,keys are a major source of single-value constraints,since
they require that associated with value(s) for the key attribute(S) are
unique values of the other attributes of the call | f*****c
发帖数: 22 | 2 Quite clear, why bother translating to Chinese?
Talk about key, single-value constraints and referenctial constraints.
Similar notion could be found on any DB text book.
【在 r****s 的大作中提到】
: keys are attributes or sets of attributes that uniquely identify an
: object within its class or an entity within its entity set.no two
: objects in a class may agree in their values for each of a set of
: attributes that constitutes a key.
: single-value constraints are requirements that the value in a certain
: role be unique,keys are a major source of single-value constraints,since
: they require that associated with value(s) for the key attribute(S) are
: unique values of the other attributes of the call
| r****s
发帖数: 12 | 3 but i can't be sure it very clearly,hehe
【在 f*****c 的大作中提到】
: Quite clear, why bother translating to Chinese?
: Talk about key, single-value constraints and referenctial constraints.
: Similar notion could be found on any DB text book.
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