LMN: Last Minute Notes For Fast Revision: DBMS
LMN: Last Minute Notes For Fast Revision: DBMS E-R Diagram: The most common asked questions in ER diagram is minimum number of tables required for a given ER diagram. Generally, following criteria are used: Cardinality Minimum No. of tables 1:1 cardinality with partial participation of both entities 2 1:1 cardinality with total participation of atleast 1 entity 1 1:n cardinality 2 m:n cardinality 3 Note: This is a general observation. Special cases need to be taken care. We may need extra table if attribute of a relationship can’t be moved to any entity side. Keys of a relation: There are various types of keys in a relation which are: Candidate Key: The minimal set of attributes which can determine a tuple uniquely. There can be more than 1 candidate key of a relation and its proper subset can’t determine tuple uniquely and it can’t be NULL. Super Key: The set of attributes which can determine a tuple uniquely. A candidate key is always a super key but vice versa is not true. Prim...
