Databases

• Data independence


  A database should act as a repository/ pool of data separate from the applications within it
• Flat-file databases


  Very basic systems that only allow a single table of data. Useful if very simple data is being recorded.
• Advantages of relational databases over flat file

  -can hold multiple tables

  -Normalised without errors associated with flat file databases
• Flat-file database


  Raw data stored in one table. Used in a simple database with very few pieces of data
• Primary key


  A field of fields that uniquely identify a record. Sometimes a composite primary key is required
• Foreign key


  When two tables are related, the primary key in one table needs to also be used as a field in the other table to form a link between them.
• Indexes

  If a field is going to be regularly used as part of a search- this can be set to indexed to allow searches to be performed
• First normal form


  No repeating attributes
• Second normal form

  Already in first normal form and each field is dependant on the whole primary key (no partial dependencies) (this only applies when there are composite primary keyS)
• 3rd normal form

  Already in second normal form and contain no non-key (transitive) dependencies
• How AND OR and IN are used in SQL

  Multiple ANDs and ORs can be combined by a list of brackets. IN can be used to specify whether a value is in a specified list
• Data independence


  A database should act as a repository/ pool of data separate from the applications within it
• Flat-file databases


  Very basic systems that only allow a single table of data. Useful if very simple data is being recorded.
• Advantages of relational databases over flat file

  -can hold multiple tables

  -Normalised without errors associated with flat file databases
• Flat-file database


  Raw data stored in one table. Used in a simple database with very few pieces of data
• Primary key


  A field of fields that uniquely identify a record. Sometimes a composite primary key is required
• Foreign key


  When two tables are related, the primary key in one table needs to also be used as a field in the other table to form a link between them.
• Indexes

  If a field is going to be regularly used as part of a search- this can be set to indexed to allow searches to be performed
• First normal form


  No repeating attributes
• Second normal form

  Already in first normal form and each field is dependant on the whole primary key (no partial dependencies) (this only applies when there are composite primary keyS)
• 3rd normal form

  Already in second normal form and contain no non-key (transitive) dependencies
• How AND OR and IN are used in SQL

  Multiple ANDs and ORs can be combined by a list of brackets. IN can be used to specify whether a value is in a specified list