What is a database?
A database is a way of storing information in a structured, logical way.
Database Models: 'Relational Model'
-- Databases consist of tables, which are linked
-- Each table has a name
-- column, row
Relational Model: attribute, tuple
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Attribute, attribute types
-- 'null' value
--constraints, for example, student number is not null, every student must have oneTables
-- an individual cell in a table --> one piece of data
-- each row has the same number and type of columns
-- each row must be unique(no duplicate rows)
Primary Keys
- A primary key is an attribute in a table which can be used to uniquely identify each row
-- you have only one primary key in a table
-- each table will normally have several potential primary keys which is called candidate keys
Database Schema
- a description of the columns in a table can be called the table schema
*example: Table(col,col,col...) Table(col,col,...)
E.g. Student(studentNumber, name, address, DOB) - Tables can be empty(no rows of data), but must have a schema
SQL = Structured Query Language
- Relational databases use SQL(structured query language) to get this information
- A standard language for accessing and manipulating information in relational databases
- The language consists of SQL commands
- SQL is an ANSI(American National Standards Institute) Standard, but there are slightly different versions(flavours)
SQL Flavours
- most implementations do not implement the entire standard
- but they all implement the basics
- Common Flavours:
Oracle, MySQL, SQLite, PostgreSQL, MSQL(Microsoft), Microsoft Access
