Oracle DBMS Interview Questions and Answers - 1
A relationship is an association between entities (or tables). It is based on having common data values in the designated columns of each table.
A relationship is defined by linking the common columns in the two tables,
Relationships are actual objects in the database.
Following are the three types of relationships:
One to one : Implies that a single records from the first table can be linked to multiple records in the second table and vice versa.
One to many: Implies that a single record form the first table can be linked to multiple records in the second table while a single record in the second table relates to only a single record in the first table.
Many to many: Implies that multiple records from the first table can be linked to multiple records in the second table and vice versa.
What is a primary key?
A primary key is an attribute (or a collection of attributes) that uniquely identifies each row in the table.
In other words, each entity instance in a table must be unique; and therefore, primary key is a way of ensuring this.
What is a foreign key?
A foreign key is an attribute in a child table that matches the primary key value in the parent table.
What is de-normalization?
OLTP databases are intended more for DML operations; therefore these databases are designed to reduce redundancy; whereas, Online Analytical Processing (OLAP) database or warehousing applications are primarily used for reporting.
OLAP databases are not used for day–to-day transactions in general and reporting performance is more critical for such database; therefore, these databases are designed to store data to support easy access without requiring too many joins.
Redundancy of data is not of much concern in these databases; therefore, tables are designed as a join of two or more tables from a typical OLTP application. This is called de-normalization.
What is full functional dependency?
Full functional dependency is the situation when an attribute depends on a group of attributes completely but not on the subset of the attributes.
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