1 votes 1 votes An instance of relational schema $R(A,B,C)$ has distinct values of $A$ including $NULL$ values. Which one of the following is true? $A$ is a candidate key $A$ is not a candidate key $A$ is a primary key Both “$A$ is a candidate key” and “$A$ is a primary key” Unknown Category nielit-scb-2020 + – gatecse asked Dec 9, 2020 • edited Dec 12, 2020 by soujanyareddy13 gatecse 643 views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes It is candidate key, because it has distinct value but it cant be primary key as primary key doesnt allow null value Bhawana nandan answered Jan 17, 2021 Bhawana nandan comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes (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 22 answered Feb 18, 2022 22 comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes They have mentioned clearly that it’s “An instance of relational schema...” And based on the instance we cannot conclude if an attribute will be CK or NOT. May be now, at this point of time, the values are distinct but it doesn’t mean that in future also it’s going to be distinct. Also, for the same reason we cannot even conclude that it’s not the CK. It may so happen that it’s the CK. Both are possible. Similar question asked in GATE: Databases: GATE CSE 1994 | Question: 3.7 (gateoverflow.in) biswajitbora answered Nov 8, 2023 biswajitbora comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes Option (B) is correct A is not a candidate key . madhurKG answered Dec 8, 2023 madhurKG comment Share Follow See all 0 reply Please log in or register to add a comment.