relational algebra-null value

Explain how relational algebra operations deal with NULL values.

5Comments
set2018 @setgate
2 Oct 2017 08:58 pm

shivani1234 explain this concept pls

shivani @shivani1234
3 Oct 2017 12:53 pm

Relational algebra consists of several operations like union , intersection , set difference , joins,..

  • Union : A ∪ NULL = A
  • Intersection : A ∩ NULL =NULL 
  • Set difference : A - NULL = A
  • Joins : Natural Join: A X NULL = NULL
    Left Join : A ⋊ NULL = null 
    Right join : A ⋉ NULL =  A
     
Akshay Saxena @akshay0612
3 Oct 2017 12:43 pm

@shivani1234 right join should be null?

 

set2018 @setgate
3 Oct 2017 02:53 pm

what about  projection ?

 

shivani @shivani1234
3 Oct 2017 03:17 pm

if column attribute has got null values , it will output as null on projection