Databases and SQL Lab EECS 448

Transcription

1 Databases and SQL Lab EECS 448

2 Databases A database is an organized collection of data. Data facts are stored as fields. A set of fields that make up an entry in a table is called a record. Server - Database StudentRecord - Table Student_GPA - Record 3324, John, Field John Servers can possess n databases Databases possess n tables Tables possess n records Records possess n fields All records in the same table have the same number of fields

3 Table Example Table name: Student_GPA Field name Field datatype StudentID (int) LastName (Text) FirstName (Text) GPA (double) 1000 Doe John Cook Dale Smith Sarah 3.3 Each row is a record Columns are fields Primary Keys 'id' here is likely defined as a Primary Key Primary Keys assert that entries are unique

4 Creating a table CREATE TABLE statement Creates a new table Expects a series of column names and data types CREATE TABLE Student_GPA (id INT, LastName TEXT, FirstName TEXT, GPA DOUBLE) Let's query the table and get all of its contents SELECT * FROM Student_GPA This returns nothing because we haven't inserted any records. To delete the table use the DROP statement DROP TABLE Student_GPA To create a table with a Primary Key constraint: CREATE TABLE Student_GPA (id INT, LastName TEXT, FirstName TEXT, GPA DOUBLE, PRIMARY KEY(id))

5 Inserting data into a table INSERT INTO statement Adds a new record to a table Expects a value for each field in the table's definition INSERT INTO Student_GPA VALUES (1000, 'Doe', 'John', 3.5); INSERT INTO Student_GPA VALUES (1001, 'Cook', 'Dale', 2.3); INSERT INTO Student_GPA VALUES (1002, 'Smith', 'Sarah', 3.3); INSERT INTO Student_GPA VALUES (1000,'McHenry','Aaron',1.6); The last statement fails because there already exists an id of 0 and id is a primary key. Now, let's query the table: SELECT * FROM Student_GPA SELECT id, FirstName FROM Student_GPA SELECT * FROM Student_GPA WHERE GPA > 3.0

6 Changing data Modify a field in a row UPDATE statement Changes fields in a table Expects a value for each field in the table's definition UPDATE Student_GPA SET GPA = 4.0 WHERE LastName = 'Smith' Query again SELECT * FROM Student_GPA Delete a record DELETE FROM statement DELETE FROM Student_GPA WHERE LastName = 'Smith' AND FirstName = 'Sarah' DELETE FROM Student_GPA WHERE id = 1002 Using the latter is probably safer for something like this because 'id' is unique

7 Relational Tables Example Class Student StudentID (int) LastName (Text) FirstName (Text) Class (int) 1000 Doe John Cook Dale 3 ClassID (int) ClassName (Text) 0 Freshman 1 Sophomore 2 Junior 3 Senior 1002 Smith Sarah 2 Primary Keys: Student.StudentID Class.ClassID Grade.GradeID Foreign Keys: Student.Class Class.Student Grade GradeID (int) Course (Text) Student (int) Grade (double) 0 Calc I Calc I Algebra Calc II

8 Querying from multiple tables Select with INNER JOIN keyword SELECT Student.FirstName, Student.LastName, Class.ClassName FROM Student INNER JOIN Class ON Student.Class = Class.ClassID This returns: Doe John Senior Cook Dale Senior Smith Sarah Junior

9 Querying from multiple tables Inner joining and taking an average SELECT Student.FirstName, Student.LastName, AVG(Grade.Grade) FROM Student INNER JOIN Grade ON Student.StudentID = Grade.Student GROUP BY (Student.StudentID) This returns: Doe John 3.5 <- 2 John Doe rows averaged here Cook Dale 4.0 Smith Sarah 3.0

10 The Rest of Lab The rest of lab is an individual assignment that will have you create a MySQL table build MySQL statements execute MySQL statements from within Java open multiple windows in a GUI application

11 Lab Assignment Start by checking out the starter code from the TA's repository File->Import..., SVN->Checkout Projects Repository: edu/jgevargi/public_folder Import Lab05_SQLLoginApp You will see that this project already has a form called 'MainForm' For this assignment you will extend this application with a login window and a registration window You will need to create a 'LoginForm' and a 'RegisterForm'

12 GUI Samples LoginForm RegisterForm MainForm (already implemented)

13 Database Requirements You will need to define one table. You can use phpmyadmin to do this Name it "Lab05_Credential" It will have three fields Username - Text Password - Text FullName - Text The LoginForm will query the table that you create to see if the Username and Password combination already exists Upon success, it should open an instance of MainForm This is a successful login and entry into the program Display a message box upon invalid login The RegisterForm will insert a new row with the specified username, password, and full name Upon registering, it should return the user to the login form

14 Multiple Windows guide Make a new 'Application Window' for the two new forms Name them 'LoginForm.java' and 'RegisterForm.java' To open a form from within another, use this code snippet: MainForm newform = new MainForm(); newform.frame.setvisible(true); This is simply creating an instance of a class and then executing a method on it To close an existing form, call the dispose() method of its frame object: frame.dispose(); In a new application window, the highest component in the hierarchy is a JFrame which is named 'frame' by default. MainForm has a method defined that allows you to pass in the user's full name Call the SetUserData() method of MainForm before showing its frame

15 Executing SQL from Java guide The following page has sample code for executing making a complete SQL transaction from Java The executes one query Adjust the code sample for the two MySQL transactions that you will make Note that in the provided code segment, the query was executed with executequery() For statements that do not return data, simply use execute() Before this code will work properly, you must setup the MySQL driver By default, the java libraries can handle SQL servers but not MySQL The driver installation is described in the page after next

16 Executing SQL from Java guide String username = "... //this is your EECS username String password = "... //this is your MySQL password String commandtext= "SELECT * FROM Table1"; //the sql statement String url = "jdbc:mysql://mysql.eecs.ku.edu/" + username; //server + database string try { Class.forName("com.mysql.jdbc.Driver"); } catch (ClassNotFoundException e) { } try { System.out.println(e.getMessage()); Connection con = DriverManager.getConnection(url, username, password); //creates a connection with the server Statement stmt = con.createstatement(); ResultSet rs = stmt.executequery(commandtext); //results get stored in a ResulSet, you may have to look up ResultSet examples and its documentation while (rs.next()) { //increments to the next row } rs.close(); stmt.close(); } catch (SQLException e) { } String address = rs.getstring("address_short"); //this is getting the column named 'Address_Short' System.out.println(e.getMessage());

17 MySQL Driver, Install Install Procedure 1. Make a directory in your home called 'jdbc' 2. Download the MySQL-Connector file from the lab page and put in the 'jdbc' directory 3. Open.bashrc in your home directory and add the following lines MYSQLDRV="mysql-connector-java bin.jar" export CLASSPATH="~/jdbc/$MYSQLDRV:." These commands will run every time you login.bashrc already exists, but it is hidden 4. To run the commands immediately, run the following bash>source.bashrc Lastly you will need to add the jar file to your eclipse project Right click the project, Build Path->Add External Jars...