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In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table. The columns in the referencing table must be the primary key or other candidate key in the referenced table. A table may have multiple foreign keys, and each foreign key can have a different referenced table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys. Improper foreign key/primary key relationships or not enforcing those relationships are often the source of many database and data modeling problems.
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Define key in dbms with example?
Supper Key- s a set of one or more attributes that taken collectively and allow us to identify entities with in entity set.
What ensures the value of the foreign key matches another tables primary key?
It is the DBMS that ensures the value of the foreign key matches another table's primary key when referential integrity constraints are enabled within the DBMS
What is secondary indexes in dbms?
secondary index is a key which is created other than primary key, to speed up processing.
Could DBMS being the key for the billionaires of the future?
k onda k onda
Definition of key in dbms?
It is a pool of data through which data are enter into into the table for data management.
Why relation have key in DBMS?
A software system that facilitates the creation and maintenance and use of an electronic database
What are the types of dbms attributes?
Types of Attributes in Dbms areKey or non key attributesRequired or optional AttributesSimple or composite AttributesSingle-valued and multi-valued AttributesStored, Coded or derived Attributes
What is the prime attribute in DBMS?
prime attributes are the attributes of a candidate key which will give uniqueness. a candidate key is (the subset of superkey) which gives uniqueness. Super key is the maximum set of attributes that can provide uniqueness example ABCDE is a super key AB CD DE are the candidate keys s.t. AB is the primary key. CD and DE are the secondary/alternate keys.
Non-prime attribute in DBMS?
Prime attribute are part of any candidate key. Non-prime attribute are not part of any candidate key.
What questions may be asked in IGNOU's BCA project viva?
DFD SDLC primary key unique key etc......... study DBMS very well and ur project
What is overlapping key DBMS?
Overlapping Key is a type of candidate key which occurs in BCNF (Boyce –Codd Normal Form).In the difference between 3NF and BCNF Example : A 3NF table which does not have multiple overlapping candidate keys is guaranteed to be in BCNF. Depending on what its functional dependencies are, a 3NF table with two or more overlapping candidate keys may or may not be in BCNF.
What is weak entity sets in dbms?
An entity set may not have sufficient attributes to form a primary key is called weak entity set. One with primary key is called strong entity set.
