3 votes 3 votes I have doubt in 3rd statement second part Nils asked Nov 13, 2017 Nils 388 views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes alternate keys can have nul values. primary keys don't have null values. raviyogi answered Nov 13, 2017 raviyogi comment Share Follow See all 3 Comments See all 3 3 Comments reply Nils commented Nov 13, 2017 reply Follow Share But unique key can have only one value as null in unique specified attribute(column). in question they specifying : unique key can hav null VALUES. ( what is difference between alternate key ,unique key & primary key,??) 0 votes 0 votes Rupendra Choudhary commented Nov 13, 2017 reply Follow Share Hello ravi , please try to answer in detailed way , and answer each and every portion. i don't think the way you provided answer would help anyone. 0 votes 0 votes raviyogi commented Nov 13, 2017 reply Follow Share Super Key is the set of one or more column (ie attributes) which uniquely identifies a record. (unique key)Candidate key is a minimal Super key.(it mean we cant remove any attributes from it otherwise it will not remain Superkey anymore). Primary Key is a arbitrary selected Candidate key that don't allow any null values. There must be only and only One primary key. We can choose any candidate key as a Primary key. Other candidate keys which are not chosen as Primary are called Alternate Keys 0 votes 0 votes Please log in or register to add a comment.
0 votes 0 votes 1)for BCNF , dependencies will be of type super key->any attribute , so we don't care what's there in right side , left side must be super key. if i talk more specific then if prime attributes are transitively dependent on key then relation will be in 3NF and every 3NF is BCNF. 2) this is must condition for 2NF , not for 3NF as even if this is satisfied then still there would be redundancy caused by non-prime->non-prime , which is eliminated in 3NF. 3) unique key is different from primary key.It can be NULL. https://en.wikipedia.org/wiki/Unique_key https://stackoverflow.com/questions/9565996/difference-between-primary-key-and-unique-key Rupendra Choudhary answered Nov 13, 2017 Rupendra Choudhary comment Share Follow See 1 comment See all 1 1 comment reply Nils commented Nov 13, 2017 i edited by Nils Nov 13, 2017 reply Follow Share thank you sir... 0 votes 0 votes Please log in or register to add a comment.
0 votes 0 votes a)false b)false c)true abhishekmehta4u answered Mar 30, 2018 abhishekmehta4u comment Share Follow See all 0 reply Please log in or register to add a comment.