database relatinship
DESCRIPTION
TRANSCRIPT
Relational database matches data by using common characteristics found within the data set.
Primary keys
Foreign keys
Relationship Types
The primary key of a relational table uniquely identifies each record in the table.
It can either be a normal attribute that is guaranteed to be unique (such as Roll No in a student Table or Employee Number in Employee Table)
A foreign key is a field in a relational table that matches the primary key column of another table.
The foreign key can be used to cross-reference tables.
A relationship exists between two database tables when one table has a foreign key that references the primary key of another table.
One-to-one: Occur when there is exactly one record in TableA that corresponds to exactly one record in TableB.
One-to-many: Occur when each record in TableA may have many linked records in TableB but each record in TableB may have only one corresponding record in TableA.
Many-to-many: Occur when each record in TableA may have many linked records in TableB and vice-versa.