Presentation on theme: "Relational Database Systems Higher Information Systems Advanced Implementation in Microsoft Access."— Presentation transcript:
Relational Database Systems Higher Information Systems Advanced Implementation in Microsoft Access
Developing a solution Tables Queries User Views Navigation
Referential Integrity For the database to work properly, it is essential to guarantee that a foreign key always refers to a record which exists in the other table. This is called referential integrity. For example, an entry in the Loan table can only refer to an existing record in the Member table, because a loan can only be made by a member.
Referential Integrity Referential integrity is established by defining relationships between the tables
Lookups are used to ensure referential integrity
Referential Integrity In the Loan table, the user can only enter a value for Member Number which already exists in the Member table
Validation: Presence Check
Validation: Range Check
Validation: Restricted Choice Check
Validation: Default Value
Queries Searching Sorting Calculations
Searching Searching is the process of selecting records from a table or combination of tables To perform the query, three items must be identified Which fields will be used to identify the records required? What are the criteria for identifying the records required? Which fields will be displayed?
Search 1: Single Condition Identify the names and telephone numbers of club members who have rented Shrek
Search 2: Multiple Conditions (AND) List those members who have rented Shrek since 16 August 2004
Search 3: Multiple Conditions (OR) List those members who have rented Shrek or Finding Nemo.
Search 3: Multiple Conditions (OR) Use Group By to eliminate duplicates
Search 4: Combining conditions List the members who have rented either Shrek or Finding Nemo since the 16 August 2004 The search criteria are: Film Title = Shrek AND Date Hired > 16/08/2004 OR Film Title = Finding Nemo AND Date Hired > 16/08/2004 Note that the Date Hired condition must be repeated for each film
Search 4: Combining conditions List the members who have rented either Shrek or Finding Nemo since the 16 August 2004
Sorting To perform a sort, two items must be identified: Which field (or fields) will be used to decide the order of records? For each field selected, will the order of sorting be ascending or descending?
Sorting To produce a list of people with the tallest first, the records would be sorted in descending order of height. To produce a list of people with youngest first, the records would be sorted in ascending order of age. A very common way of ordering records relating to people is in alphabetical order. To achieve alphabetical ordering requires the records to be sorted in ascending order of surname.
Complex Sorting A complex sort involves more than one sort condition involving two or more fields. To achieve telephone book order, the name is sorted in ascending order of surname, then ascending order of forename. In this case, the Surname field is the primary sort key, and the Forename field is the secondary sort key.
Calculations Horizontal calculations are often known as calculated fields, and vertical calculations are known as summary fields.
Working with Dates to search for all DVDs rented in the last week, you would use the expression Date() – [Date Hired] <= 7 to calculate a persons age in years from their date of birth, you would use the expression DateDiff("yyyy",[Date of Birth],Date())
User Views User views are created using forms and reports. A form or report is usually based on a query which selects the required fields from the appropriate tables, sorting the results if necessary, and performing any horizontal calculations.
Summary Information Sumto add values to give a total, e.g. Total Cost of DVD Rentals last month Averageto find an average value, e.g. Average Cost of Hire per DVD Countto count the number of records found, e.g. Number of DVDs rented per member Maximumto find the highest value, e.g. Highest number of rentals per DVD (to find the most popular DVD) Minimumto find the lowest value, e.g. Lowest number of rentals per member
Summary Information Summary information is produced by creating a summary field. A summary field is a calculated field with a formula to perform the calculation, and is placed in a summary section of a report.