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An instance of relational schema $R(A,B,C)$ has distinct values of $A$ including $NULL$ values. Which one of the following is true?

  1. $A$ is a candidate key
  2. $A$ is not a candidate key
  3. $A$ is a primary key
  4. Both “$A$ is a candidate key” and “$A$ is a primary key”
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It is candidate key, because it has distinct value but it cant be primary key as primary key doesnt allow null value
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(A) A is a candidate key ...

Key Points ::

1. The primary key can not have a NULL value....

2. The candidate key can have a NULL value ..…

 

1. https://csedoubts.gateoverflow.in/26837/nielit-nic-scientist-b-2020-set-c-ques-48

 

 

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