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Transcript
Databases and modelling 3. day Agenda • • • • • Introduction to SQL Status on database implementation Forms Exercises Reports 2 Introduction to SQL • SQL = Structured Query Language • (DML – Data Manipulation Language included) • A declarative programming language (telling the computer what to do – not how to do it by means of algoritms like imperative programming languages) SQL tells the database management system what to do and to do the actual changes and retrievals in the database • Developed as part of the development of relational databases • SQL is in slightly different versions implemented in databases as MySQL, PostgreSQL, Oracle databases and MS Access 3 What SQL does • SQL (+DML) can execute queries retrieve data from a database insert new records in a database delete records from a database update records in a database • Example (see the difference?) SELECT author.ID, author.Author FROM author; SELECT book.[Book number], book.[Book title] FROM book; 4 SQL Statements • SELECT - extracts data from a database table • UPDATE - updates data in a database table • DELETE - deletes data from a database table • INSERT INTO - inserts new data into a database table • SELECT LastName,FirstName FROM Persons 5 SQL Example SELECT book.[Book number], book.[Book title] FROM book; SELECT table_name.[field name], table_name.[field name 2] FROM table name; SELECT book.[Book title], book.[Book number] FROM book WHERE (((book.[Book number])=1)); SELECT author.Author, book.[Book title] FROM book INNER JOIN (author INNER JOIN [Written by] ON author.ID = [Written by].Author) ON book.[Book number] = [Written by].Book; 6 SQL exercise • Write SQL expression that extracts book title, publication year and publisher from the book table • Find publications from 2006 only 7 Step 6 8 Example 9 Different kinds of forms • Forms for displaying data • Form for navigating data • Forms for user dialog and search (combined with queries) 10 Exercise - forms • Analyse the Northwind database How does the main switchboard call other forms? Orders form: How does the content in the Bill to dropdown come from? Important and often easier to learn (and copy…) from something already working 11 Reports • Pulling data out of the database formatted for other media 12