Chapter 5

Chapter 5

Database components
1. Table - data structured into rows and columns requires a primary key
2. Records - a single row within a table made up of individual fields
3. Field - An individual data item within a record
4. Key - a field used for identification
  1. Primary - allows a record to be uniquely identified. Can be combined to make a composite key
  2. Secondary - a field which can be used to index data
  3. Foreign key - a field which is linked to the primary key in another table or entity
5. Entity - A Thing which can be identified, a logical or physical storage unit
Relationships
1. One-to-one
  1. One instance of X to one instance of Y
  2. Uncommon
2. One-to-many
  1. Common
  2. One instance of X relates to many instances of Y
3. Many-to-many
  1. Foreign key on many side and primary on the one
  2. Many instances of X relate to many instances of Y
Normalisation
1. 1NF
  1. Primary key
  2. Unique field names
  3. no repeating fields
  4. Atomic fields
2. 3NF
  1. All 2NF conditions met
  2. All non-key fields are dependent on the primary key
3. 2NF
  1. All 1NF conditions met
  2. All of the non-key attributes can be found using the primary key
Data dictionary
1. Defines aspects of a database
2. e.g. Table name Keys Relationships
Queries
1. Static - Predefined parameters
2. Dynamic - Parameter input on each run
3. Simple - Only one parameter
4. Complex - multiple parameters
  1. AND
  2. OR
  3. NOT
  4. *xyx*
  5. x* (starts)
  6. *x (ends)
  7. Standard mathematical operators

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	Criado por green.george quase 13 anos atrás