Explain the features of a relational database (P1)
A relationship is a defined connection between the rows of two tables. This connection is general determined by values in selected columns from the parent table that correspond to values in the child table.
A one-to-many relationship is when a parent record in one table can potentially reference several child records in another table. In a one-to-many relationship, the parent is not required to have child records; therefore, the one-to-many relationship allows zero child records, a single child record or multiple child records (the child record cannot have more than on parent record).
A one-to-one relationship I when a record in one table is linked to only one other record in another table. A record cannot link to more than one record in another table, it must only link to one. The number of rows in Table A must equal the number of rows in Table B.
A many-to-many relationship is when on ore more rows in a table are associated with one or more rows in another table. An example of this I that a table of customers who can purchase many different products and a table of products that can be purchased by many different customers.
Normalisation is the process of organising data in a database. This includes creating tables and establishing relationships between those tables according to rules designed both to protect the data and to make the database more flexible by eliminating redundancy and inconsistent dependency.
Businesses can use attributes to help them. This can be done by identifying the most important factors. For example, ‘Name, address, postcode etc.’ and then putting them in entities.
Text or alphanumeric data is made up of letters and/or numbers. Also symbols and spaces are also allowed into this data type.
Address: 123 Sample Street
Number or Numeric data is made up of whole numbers or decimal numbers to be used. Only numbers can be entered and not letters or symbols.
Height (cm): 172.8
Currency data type automatically formats the data to have a £ or $