Chapter 8 Databases

Objectives Explain the structure of a relational database Use SQL for creating, maintaining, and accessing relational databases Use Java/JDBC for accessing relational databases Explain and apply basic principles of good database design

RDBMS A Relational Database Management System (RDBMS) provides data storage and access for web applications

Relation relation is a mathematical term that refers to an ordered set of values drawn from different domains Ex: a relation on numbers x letters x symbols (55, A, #)

Database Structure A database includes one or more tables Each table represents one type of entity Example: Tables in a Library Database Patron Loan (transaction) Recording Book

Database Structure Each table field represents an entity attribute Each table row represents one entity Car table: Year Make Model Color 1973 Volkswagen Jetta Red 1992 Ford Aerostar Blue 2004 Chevrolet Suburban Black row field

Structured Query Language SQL is a standard language for creating and maintaining relational databases SQL statement types: data definition: create databases and tables data manipulation: add, modify, delete data data control: set access permissions

Basic SQL Statements Data definition Data manipulation Data control CREATE, DROP Data manipulation SELECT, INSERT, UPDATE, DELETE Data control GRANT, REVOKE

CREATE Create a database or a table CREATE DATABASE ehsl CREATE ehsl.player ( playerNr int PRIMARY KEY, name VARCHAR(30), isCurrent BOOLEAN NOT NULL)

Basic SQL Data Types INTEGER DECIMAL(T, R) FLOAT CHAR(N) N characters T=total digits, R=right digits (after '.') FLOAT CHAR(N) N characters VARCHAR(N) up to N characters BOOLEAN DATE TIME

DROP DROP can be used to delete an entire database or a table DROP ehsl DROP ehsl.player

SELECT SELECT retrieves data from a database SELECT field-list FROM database.table WHERE condition ORDER BY field-list field-list is a comma-separated list of fields from the named table (* means "all fields") condition is a Boolean condition using field names and/or constants

SELECT Example SELECT * FROM ehsl.player SELECT playerNr, name FROM ehsl.player WHERE isCurrent=TRUE SELECT playerNr, name, status FROM ehsl.player WHERE playerNr >= 90001 ORDER BY status, name

INSERT INSERT adds a new row to a table INSERT INTO ehsl.player VALUES (23752, 'Jane Doe', TRUE)

UPDATE UPDATE changes one or more rows UPDATE database.table SET field-assignment-list WHERE condition UPDATE ehsl.player SET isCurrent=TRUE WHERE playerNr=33256

DELETE DELETE removes one or more rows from a table DELETE FROM database.table WHERE condition DELETE FROM ehsl.player WHERE playerNr=33523

Warning UPDATE and DELETE without a WHERE clause will affect all rows! UPDATE ehsl.player SET isCurrent=true DELETE FROM ehsl.player Change all rows! Delete all rows!

GRANT GRANT can be used to give access permissions to users GRANT ALL PRIVILEGES ON database.table TO user-name user-name is formatted as user@host, for example 'jonesac'@'localhost'

REVOKE REVOKE can be used to eliminate access permissions REVOKE ALL PRIVILEGES on database.table FROM user-name REVOKE ALL PRIVILEGES on ehsl.player FROM 'jonesac'@'localhost'

Create User The CREATE command can also be used to create new users CREATE USER user-name IDENTIFIED BY password CREATE USER 'jonesac'@'localhost' IDENTIFIEC BY 'abc123#'

JDBC Java Database Connectivity (JDBC) is a Java API that allows Java programs to interact with relational database management systems Interaction also requires a database driver, which translates JDBC commands to procedure calls on the RDBMS RDBMS Application Program Driver JDBC

JDBC – Load Driver The first step is to load the database driver Usually provided by the RDBMS vendor String driverClassName = "com.mysql.jdbc.Driver"; try { Class.forName(driverClassName); } catch (ClassNotFoundException cnfe) { ….

JDBC – Execute Query (1/2) To execute an SQL Query: String query = "..."; Vector<String> colNames = new Vector<String>, result = new Vector<String>; try { Connection con = DriverManager.getConnection( dbUrl, dbUserId, dbPassword); Statement st = con.createStatement(); ResultSet rs = st.executeQuery(query); ResultSetMetaData md = rs.getMetaData();

JDBC – Execute Query (2/2) To execute an SQL Query: // get column names for (int i = 1; i <= md.getColumnCount(); i++) { colNames.addColumnName(md.getColumnName(i)); } // get field values while (rs.next()) { for (int i = 1; i<=md.getColumnCount(); i++) { result.addFieldValue(rs.getString(i)); con.close(); } catch (SQLException s) { ... access the next row of the table access the next field of the row

JDBC – Execute Command To execute an SQL command: int result = 0; String command = "..."; try { con = DriverManager.getConnection( dbUrl, dbUserId, dbPassword); stmt = con.createStatement(); result = stmt.executeUpdate(command); con.close(); } catch (SQLException s) { ... } result = number of rows affected (inserted, modified, or deleted)

JDBC Design An effective design for database access: JSP: user interface presentation Java Servlet: application logic Java Bean: database access (JDBC) Java Bean access RDBMS using JDBC JSP create user interface dependency RDBMS Java Servlet process / prepare data

Database Design Principles Each field should contain a single value Repeated fields with empty values should be made a separate table Each table should represent only one entity

Example: Registration multiple valued field WRONG: Better: empty fields

Example: Registration Better still: multiple entities: class registration / class name

Example: Registration RIGHT:

Review Relational Database / RDBMS SQL JDBC Database Design Principles Data Definition Data Manipulation Data Control JDBC Database Driver Query Execution Command Execution Database Design Principles