Relational databases
What is a primary key
A primary key is a field in a table which is unique and enables you to identify every record in that table.
What is a composite key
A composite key, in the context of relational databases, is a combination of two or more columns in a table that can be used to uniquely identify each row in the table. Uniqueness is only guaranteed when the columns are combined; when taken individually the columns do not guarantee uniqueness.
attribute definition
In general, an attribute is a characteristic. In a database management system (DBMS), an attribute refers to a database component, such a table. It also may refer to a database field. Attributes describe the instances in the row of a database
What are advantages of RDBs
RDB performs "select", "project" and "join" database operations, where select is used for data retrieval, project identifies data attributes, and join combines relations. RDBs have many other advantages, including: •Easy extendability, as new data may be added without modifying existing records. This is also known as scalability. •New technology performance, power and flexibility with multiple data requirement capabilities. •Data security, which is critical when data sharing is based on privacy. For example, management may share certain data privileges and access and block employees from other data, such as confidential salary or benefit information.
How do RDBs organize data
RDBs organize data in different ways. Each table is known as a relation, which contains one or more data category columns. Each table record (or row) contains a unique data instance defined for a corresponding column category. One or more data or record characteristics relate to one or many records to form functional dependencies. These are classified as follows: •One to One: One table record relates to another record in another table. •One to Many: One table record relates to many records in another table. •Many to One: More than one table record relates to another table record. •Many to Many: More than one table record relates to more than one record in another table.
Explain the concept of a relational database
A relational database (RDB) is a collective set of multiple A relational database (RDB) is a collective set of multiple data sets organized by tables, records and columns. RDBs establish a well-defined relationship between database tables. Tables communicate and share information, which facilitates data searchability, organization and reporting. RDBs use Structured Query Language (SQL), which is a standard user application that provides an easy programming interface for database interaction. RDB is derived from the mathematical function concept of mapping data sets and was developed by Edgar F. Codd.
what is referential integrity
Referential integrity is a relational database concept, which states that table relationships must always be consistent. In other words, any foreign key field must agree with the primary key that is referenced by the foreign key.
What is a foreign key
a foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table. In simpler words, the foreign key is defined in a second table, but it refers to the primary key in the first table. For example, a table called Employee has a primary key called employee_id. Another table called Employee Details has a foreign key which references employee_id in order to uniquely identify the relationship between both the tables.