0 votes 0 votes 1.A primary key cannot be NULL (Any of its attributes can’t be NULL) 2.can candidate key be NULL(All attr) (Other than primary keys i,e alternate keys) 3.can some attributes of candidate key be NULL?? which of these are true . false Databases databases + – jatin khachane 1 asked Jan 14, 2019 jatin khachane 1 980 views answer comment Share Follow See all 7 Comments See all 7 7 Comments reply jatin khachane 1 commented Jan 14, 2019 reply Follow Share @anjali007 @Shubhgupta 0 votes 0 votes Shubhgupta commented Jan 14, 2019 reply Follow Share 1)true, yes primary key and its attribute can't be null. (from set of candidate key which are not null and unique is primary key.) 2) true, other than primary key there can be multiple candidate key and that can be null and called as alternate key. but remember there should be one primary key exists in relation which is not null and uniquely identify the rows. 3) true, as stated above. 0 votes 0 votes anjali007 commented Jan 14, 2019 reply Follow Share Primary keys cant be null So statement 1 is true.. regarding the other candidate keys which are not selected as primary key they can be null .. Primary keys cant be null because of uniqueness constraint .If primary key is null then 2 or more nulls will voilate the uniqueness constraint so they are not null...So all 3 are true... 0 votes 0 votes jatin khachane 1 commented Jan 14, 2019 reply Follow Share Can some attributes of candidate key be NULL?? @Shubhgupta we call attributes of Candidate key as prime attribute as well right ? And prime attribute can't be null right ? 0 votes 0 votes Shubhgupta commented Jan 14, 2019 reply Follow Share in that case candidate key termed as primary key where prime can not be null otherwise it termed as alternate key. A prime attribute is a part of candidate key where key is primary key. 0 votes 0 votes jatin khachane 1 commented Jan 14, 2019 reply Follow Share can you explain little more about candidate key and alternate keys which can be null and which not ...it so confusing for me :( 0 votes 0 votes anjali007 commented Jan 14, 2019 reply Follow Share see primary key cant be null ..candidate keys other than the primary key may be null i.e alternate keys may be null 0 votes 0 votes Please log in or register to add a comment.
0 votes 0 votes Primary key cannot be Null but Candidate key apart from Primary key may have Null values Sanandan answered Aug 23, 2020 Sanandan comment Share Follow See all 0 reply Please log in or register to add a comment.