[a] The relations of two sub-entity sets of the same super entity set have 1- Th

Question

[a] The relations of two sub-entity sets of the same super entity set have 1- The same keys 2- The same attributes 3-The same constraints 4- The same natural joins with their super entity set 5- All of the above 6- None of the above b] The condition A B in a WHERE clause of an SQL query, where A is an attribute in relation R and B an attribute in relations S, is true 1- For all values of A and B where A B 2-For all values of A and B where A = B except when A has a NULL value 3-For all values of A and B where A = B except when B has a NULL value 4-For all values of A and B where A = B except when A and B have NULL values 5- All of the above 6- None of the above [c] The condition A

Explanation / Answer

Answer is as follows:

a) The correct option is 1 i.e. only keys are same

Becasue sub entities can have same or different attributes both and can different constriants also. But the keys are same in this.

b) The correct optioin is 4 i.e. A = B except A and B has NULL values ,

because this implements only on common keys that have same types of data and operated on primary keys So they can't have null values.

c) The correct option is 1 i.e. A <=B

Because for every value of A can be less than or equal to B is True here. it got false if A gets greater than B.

So we not bother abput here NULL values

d) The correct option is 1.

The condition is True if both values can't match.

e) The correct option is 2.

It will change only when data in Attribute A is changed.

if there is any query please ask in comments...

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