Database - mysql

Contents

Database – DBMS– Relational model

SQL– MySQL

Database

Database– a collection of data– Entity, relationship

DBMS– Database management system

DBMS

Why use a DBMS?– efficient access – reduced application development

time– data integrity and security– concurrent access– recovery from system crash

Relational model

Most widely used data model Relation

– A set of records– Schema

• Name of a relation, name of each fields

– Instance• A table with rows and columns

Students(sid:string, sname:string, snum:integer)

sid sname snum

euny Chang Eun Young 99

cavalist Ryu Han Seung 99

netj Jaeho Shin 00

Fields (attributes, columns)

Tuples (records, rows)

Field names

SQL

Structured query languageStandard language for interacting

with a DBMSData definitionManipulation

MySQL

Connect– mysql [–h host] [–u user] [–p[password]] [dbname]

>mysql -u root -p test

Enter password: ********

Welcome to the MySQL monitor. Commands end with ; or \g.

Your MySQL connection id is 14 to server version: 3.23.34a

Type 'help;' or '\h' for help. Type '\c' to clear the buffer

mysql>

MySQL

Data definition

– CREATE/DROP DATABASE dbname;– SHOW DATABASES;– USE dbname;

– CREATE TABLE table_name (field_name type,.., constraints,..);

– SHOW TABLES;– SHOW COLUMNS FROM table_name;– DROP TABLE table_name;

MySQL

Data manipulation

– INSERT INTO table_name [(field_name,..)]

VALUES (value,..);

– DELETE FROM table_name WHERE condition;

– UPDATE table_name SET field_name=value,.. [WHERE condition];

MySQL

Data manipulation(2)

– SELECT field_name [as field_name],.. FROM table_name [WHERE condition] [ORDER BY field_name];

– =, <, >, AND, OR, NOT (field_name LIKE “_%….”)

MySQL

ALTER TABLE

– ALTER TABLE table_name [RENAME new_table_name]/ [ADD field_name type]/ [DROP field_name]/ [CHANGE name new_name new_type];

mysql> show databases;

+----------+

| Database |

+----------+

| mysql |

| test |

+----------+

2 rows in set (0.00 sec)

mysql> use test;

Database changed

mysql> create database test2;

Query OK, 1 row affected (0.00 sec)

mysql> CREATE TABLE Students(

-> sid VARCHAR(8) NOT NULL,

-> sname VARCHAR(20),

-> snum INT,

-> PRIMARY KEY(sid));

Query OK, 0 rows affected (0.01 sec)

MySQL Data Types

Type Size Description

inttinyint,smallint,mediumint,bigint

4 bytes1,2,3 and 8 bytes

2^32 values

floatdouble

4 bytes8 bytes

Date 3 bytes In the format of YYYY-MM-DD

Time 3 bytes In the format of HH:MM:SS

char[length]varchar[length]

fiString length + 1 byte

Fixed length stringVariable length from 0 to 255 characters long

mysql> show tables;+----------------+| Tables_in_test |+----------------+| students |+----------------+1 row in set (0.00 sec)

mysql> show columns from students;+-------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-------+-------------+------+-----+---------+-------+| sid | varchar(8) | | PRI | | || sname | varchar(20) | YES | | NULL | || snum | int(11) | YES | | NULL | |+-------+-------------+------+-----+---------+-------+3 rows in set (0.01 sec)

Primary KeyPrimary Key is a column or set of columns Uniquely identifies the rest of the data in

any given row.

For Example: in the employee table, employee number is the primary key.

Foreign Key

A foreign key is a column in a table

This column is a primary key of another table

Any data in a foreign key column must have corresponding data in the other table

Foreign Key

The goal of using foreign keys is that tables can be related without repeating data

Note that foreign keys in SQL are used to check and enforce referential integrity, not to join tables. If you want to get results from multiple tables from a SELECT statement, you do this by performing a join between them:SELECT * FROM t1, t2 WHERE t1.id = t2.id;

employer

Create table with foreign keys

create table employee2 (empno smallint(4) not null, salary float,primary key (empno)) type = innodb;

create table employer (id smallint(4), employee_no smallint(4), index employ_ind (employee_no), foreign key(employee_no) references employee2(empno) on delete cascade) type=innodb;

empno (PK)

salary

100 200.85

200 129.54

300 98.17

id employee_no(FK)

51 100

52 100

53 200

54 300

employee2

MySQL Table Types

If we want to use Foreign Key– InnoDB tables

Otherwise– Default table type, MyISAM

In SQL queries you can freely mix InnoDB type tables with other table types of MySQL, even within the same query.

mysql> INSERT INTO Students -> VALUES ('euny', 'Chang Eun-young', 99);Query OK, 1 row affected (0.00 sec)…

mysql> SELECT * FROM Students;+----------+-----------------+------+| sid | sname | snum |+----------+-----------------+------+| euny | Chang Eun-young | 99 || cavalist | Ryu Han Seung | 99 || netj | Jaeho Shin | 2000 |+----------+-----------------+------+3 rows in set (0.00 sec)

mysql> DELETE FROM Students -> WHERE sid='euny';Query OK, 1 row affected (0.00 sec)

mysql> UPDATE Students -> SET sid='asdf' -> WHERE sid='euny';Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM Students;+----------+-----------------+------+| sid | sname | snum |+----------+-----------------+------+| asdf | Chang Eun-young | 99 || cavalist | Ryu Han Seung | 99 || netj | Jaeho Shin | 2000 |+----------+-----------------+------+1 row in set (0.00 sec)

mysql> SELECT * FROM Students ORDER BY sname;+----------+-----------------+------+| sid | sname | snum |+----------+-----------------+------+| asdf | Chang Eun-young | 99 || netj | Jaeho Shin | 2000 || cavalist | Ryu Han Seung | 99 |+----------+-----------------+------+3 rows in set (0.02 sec)

mysql> SELECT sname FROM Students WHERE snum=99;+-----------------+| sname |+-----------------+| Chang Eun-young || Ryu Han Seung |+-----------------+1 row in set (0.00 sec)

Using Connector/J

MySQL Connector/J is a native Java driver that converts JDBC (Java Database Connectivity) calls into the network protocol used by the mySQL database.

It lets developers working with the Java programming language easily build programs and applets that interact with MySQL and connect all corporate data, even in a heterogeneous environment.

MySQL Connector/J is a Type IV JDBC driver and has a complete JDBC feature set that supports the capabilities of MySQL.

Using Connector/J Download the software from http://dev.mysql.com/downloads/connector/j/5.0.html

MySQL Connector/J is distributed as a zip or .tar.gz archive containing the sources, the class files, and the JAR archive named mysql-connector-java-[version]-bin.jar

Install this file in C:\Program Files\Java\jdk1.5.0_07\jre\lib\

ext or similar directory on your machine

Accessing mySQL from a servlet<HTML><BODY><TITLE>See Account Information</TITLE>Enter account number to view:<BR><form action="StudentList" method="post"> <input name="account"> <input type="submit" name="submit"

value="submit"></form></BODY></HTML>

Accessing mySQL from a servletpackage dbpackage;import java.io.*;import java.sql.*;import javax.servlet.*;import javax.servlet.http.*;

public class StudentList extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

response.setContentType("text/html"); PrintWriter out = response.getWriter(); String docType = "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " + "Transitional//EN\"\

n"; String title = "Student List in mySQL"; out.print(docType + "<HTML>\n" + "<HEAD><TITLE>" + title + "</TITLE></HEAD>\n" + "<BODY BGCOLOR=\"#FDF5E6\"><CENTER>\n" + "<H1>Database Results</H1>\n");

Accessing mySQL from a servlet String driver = "com.mysql.jdbc.Driver";

String url = "jdbc:mysql://localhost/newdb"; String username = "ira"; String password = "mypassword"; String query = "SELECT * from student;"; showTable(driver, url, username, password, query, out); out.println("</CENTER></BODY></HTML>"); }

public void showTable(String driver, String url, String username, String password,

String query, PrintWriter out) { try { // Load database driver if it's not already loaded. Class.forName(driver); // Establish network connection to database. Connection connection = DriverManager.getConnection(url, username,

password); // Look up info about the database as a whole. DatabaseMetaData dbMetaData = connection.getMetaData(); out.println("<UL>"); String productName = dbMetaData.getDatabaseProductName(); String productVersion = dbMetaData.getDatabaseProductVersion(); out.println(" <LI><B>Database:</B> " + productName + " <LI><B>Version:</B> " + productVersion + "</UL>");

Accessing mySQL from a servletStatement statement = connection.createStatement(); // Send query to database and store results. ResultSet resultSet = statement.executeQuery(query); // Print results. out.println("<TABLE BORDER=1>"); ResultSetMetaData resultSetMetaData =

resultSet.getMetaData(); int columnCount = resultSetMetaData.getColumnCount(); out.println("<TR>"); // Column index starts at 1 (a la SQL), not 0 (a la Java). for(int i=1; i <= columnCount; i++) { out.print("<TH>" + resultSetMetaData.getColumnName(i)); } out.println(); // Step through each row in the result set. while(resultSet.next()) { out.println("<TR>"); // Step across the row, retrieving the data in each // column cell as a String.}

Accessing mySQL from a servletfor(int i=1; i <= columnCount; i++) { out.print("<TD>" + resultSet.getString(i)); } out.println(); } out.println("</TABLE>"); connection.close(); } catch(ClassNotFoundException cnfe) { System.err.println("Error loading driver: " + cnfe); } catch(SQLException sqle) { System.err.println("Error connecting: " + sqle); } catch(Exception ex) { System.err.println("Error with input: " + ex); } }

}

Accessing mySQL from a servletprivate static void showResults(ResultSet results) throws SQLException { while(results.next()) { System.out.print(results.getString(1) + " "); } System.out.println(); }

private static void printUsage() { System.out.println("Usage: PreparedStatements host " + "dbName username password " + "vendor [print]."); }

public void doPost(HttpServletRequest inRequest, HttpServletResponse outResponse)

throws ServletException, IOException { doGet(inRequest, outResponse); }