A Level Computer Science Paper 1: 1.3.2 Databases
A database is an organised system for storing and managing data efficiently. It ensures data accuracy, accessibility, and security, with information structured in tables containing fields that define specific data attributes.
Database
An organised collection of data
Key Terms
Database
An organised collection of data
Database advantages
Make data available to users, the data is correct and the data can be held securely
Table
A collection of associated data stored within a database
Fields
The characteristics of each table
Record
An individual entry that belongs in a table
Entity
Something in the real world that we store data about
Becomes a table in a database
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| Term | Definition |
|---|---|
Database | An organised collection of data |
Database advantages | Make data available to users, the data is correct and the data can be held securely |
Table | A collection of associated data stored within a database |
Fields | The characteristics of each table |
Record | An individual entry that belongs in a table |
Entity | Something in the real world that we store data about Becomes a table in a database |
Attribute | A characteristic of an entity Becomes a field in a database |
Entity description format | TableName(Entity1, Entity2…) |
Char(n) vs VarChar(n) | A char string has fixed length n, a varchar string has variable length up to n |
How to access a database | Using a DBMS (Database Management System) |
Flat file database | A database comprised of a single table, based around a single entity and its attributes |
Flat file advantages and disadvantages | + simple and quick to set up - very inefficient, used for storing small amounts of data |
| Databases split into multiple tables linked by relationships |
Primary key | A field in a record which is unique, allowing each record to be uniquely identified. Must not be duplicated or reused. |
Secondary key | A field can be defined as a secondary key to be indexed for faster lookups. |
Foreign key | The key in a table that correlates to a primary key in another table |
Entity Relationship Diagrams (ERD) | One to one is linked by a straight line |
SQL | Structured Query Language A declarative language used for querying and updating tables in a relational database |
SQL Queries | Retrieves data based on a given criteria |
SQL Clauses | Filters data and returns data that fulfils a specific condition |
SQL Predicates | Specify conditions which return the filter |
SQL Expression | A combination of one or more values, functions and operators |
SQL Select format | SELECT lists the fields to be displayed |
SQL UPDATE | Modifies existing values in a table |
SQL DELETE | Deletes existing records from a table |
SQL DROP | Deletes a database or table | DROP table tableName |
SQL INSERT INTO | Inserts new records into a table | INSERT INTO Table(Fields), VALUES (Data) |
Join | Combines rows from 2 or more tables based on a related column between them |
INNERJOIN | The SQL for joining tables | INNERJOIN newTableName on table.field = table.field |
SQL UPDATE Syntax | UPDATE tableName SET field = newValue WHERE … |
SQL Additional Data Types | TIME and CURRENCY |
SQL Select All | SELECT * |
SQL Like | Like "%xx%" | Where the string xx is included anywhere in the data it is returned |