Relational Databases

Question 1

Explain Relational Databases

Answer 1

• on of the most popular types of DBMS

• Def: A collective set of multiple sets of data that is carefully organised in tables, records & columns

• Table in a database communicate & share data that makes it possible for effective data search, organisation & reporting

• RDBs use STRUCTURED QUERY LANGUAGE (SQL) which is a STANDARD USER APPLICATION that provides an easy programming interface for data interaction

Question 2

What does a RDB contain (Structure of a Database)

Answer 2

• A relational database contains tables; these tables are related to each other by the data they contain
• A table is organised by rows & columns. They are the primary form of data storage in a RDB

Question 3

What is an Entity? (Structure of a Database)

Answer 3

• A group represented by a table/ Each table represents a group called an entity

Question 4

What does a table contain? (Structure of a Database)

Answer 4

• A table contains RECORDS (a series of fields) & a TUPLE is a record (a single record). These contain ATTRIBUTES which are the field names

Question 5

Explain What Keys in a RDB do & how they are used. & list the 3 main types of keys

Answer 5

1. What they do in a RDB: keys are crucial to table structure. They ensure that each record in a table is uniquely identified
2. How they are used: Keys are used to enforce integrity & identity the relationship between the tables
3. Three main types of keys:
   • Primary Key
   • Candidate Key
   • Foreign Key

Question 6

Primary Key

Answer 6

• this is a special RDB table column (or a combination of columns) designed to uniquely identify each record
• A Primary Key:
  • Must NOT contain a NULL value
  • Must contain a UNIQUE VALUE for each row of data (record) eg. ID column

Question 7

Candidate Key

Answer 7

• This is a column or a set of columns in a table that can uniquely identify any databases record without referring to any data

Question 8

Foreign Key

Answer 8

• usually a Primary Key from one table that appears in another table where the first table has a relationship with the second table