Java and Databases

CS-328Dick Steflik

Database Drivers

• Think of a database as just another device connected to your computer

• like other devices it has a driver program to relieves you of having to do low level programming to use the database

• the driver provides you with a high level api to the database

ODBC

• Open Data Base Connectivity• Developed by Microsoft for the Windows

platform as the way for Windows applications to access Microsoft databases (SQL Server, FoxPro, Access)

• Has become an industry standard• Most data base vendors supply native, odbc,

and jdbc drivers for their data base products

JDBC Architecture

Java Application

JDBC API

Data Base Drivers

Access SQL

Server

DB2 Informix MySQL Sybase

JDBC Driver Types

• Type 1– JDBC-ODBC Bridge

• Type 2– Native API, partially java

• Type 3– JDBC Network Driver, partially java

• Type 4– 100% Java

Type 1 Drivers

• Translate JDBC into ODBC and use Windows ODBC built in drivers

• ODBC must be set up on every client – driver must be physically on each machine for both

java applications and applets– for server side servlets ODBC must be set up on web

server• driver sun.jdbc.odbc.JdbcOdbc provided by

JavaSoft with JDK

Type 1 Driver (cont.)

Client JDBC-ODBC

ODBC DB

Vendor Library

Type 2 Drivers

• Converts JDBC to data base vendors native SQL calls

• like Type 1 drivers; requires installation of binaries on each client

Type 2 Drivers (cont.)

Client JDBC

Vendor Library

DB

Type 3 Drivers

• Translates JDBC to a DBMS independent network protocol

• Typically talks directly with a middleware product which in turn talks to the RDBMS– Jaguar, DBAnywhere, SequeLink

• Most flexible driver type• all java

Type 3 Drivers (cont.)

Client JDBC Vendor Middleware

DB

Tier 1 Tier 2 Tier 3

Type 4 Drivers

• Converts JDBC directly to native API used by the RDBMS

• compiles into the application , applet or servlet; doesn’t require anything to be installed on client machine, except JVM

• handiest driver type

Type 4 Drivers (cont.)

Client JDBC DB

Structured Query Language

• Developed by C. Date for Relational Data Base Management Systems (RDBMS)

• Simple Declarative Language– has no program control statements

SQL

• Two categories of commands– Data Manipulation Commands

• deal with:– RETRIEVING DATA– MAINTAINING DATA (ADDING,

UPDATING,DELETING

– Data Definition Commands• DEAL WITH:

– CREATING DATABASE OBJECTS (TABLES,VIEWS)– Object organization and attributes

Referential Integrity

• Rules to insure that table data stays accurate and accessible– rows in a table should be unique

• one column should contain no duplicate data• primary key

– column values cannot contain repeating groups or arrays

– null is different than space and zero, 2 null values are not considered equal

Data Manipulation Commands

• Select - query and display data from a database

• Insert - a new row into a table• Update - modify a column in a table• Delete a row from a table

Select

• Select (column list) from (sources) where (conditions) order by (ocolumn list)• column list - comma separated list of names of columns to be in output

– Ex. ssn , lastname , firstname,gpa– can contain literals to be included in output

• Ex. Ssn,”~”,lastname,”~”,firstname

• sources - name(s) of table(s) to retrieve data from• conditions (optional) - conditions for selections

– lastname like “S%”– (lastname = “Steflik) and (firstname like “R%”)

• ocolumn list (optional)- list of columns that output should be ordered by• Ex

– select * from student– select lastname,fristname from student where gpa > 3.0– select lastname,firstname from student order by lastname,firstname

Select - joined tables

• Two tables may be joined and viewed as a single data source is the both have a common column

• suppose we have 2 tables: Inventory and category and each has a column called catg_code

• In category catg_code is unique and is the primary key

Select - joined tables (cont.)

P_no Catg_code qty Catg_code descr

Inventory Category

join

Select - joined tables (cont.)

• To retrieve all of the part numbers and the name of the category to which the part belongs:

– select inventory.p_no category.descr from inventroy , category– select a.p_no,” “,b.descr from a inventory , b category

Insert

• Add a row to a table– insert into category values(“IGN”,”Ignition System”)

• use jdbc execute Update method– ex. Stmt.executeUpdate(“insert into Category values(‘IGN’,’Ignition System’)”);

Update

• Modify an existing row in a table– update category set descr = “Ignition Subsystem” where catg_code = “IGN”

• Use jdbc executeUpdate method – String s = “update category set descr = ‘Ignition Subsystem’ where catg_code =

‘IGN’ ”;– stmt.executeUpdate(s);

Delete

• Remove a row from a table– delete from category where catg_code = “IGN”

• remove the IGN category– delete from category where catg_code like “I%”

• remove all rows where catg_code starts with an “I”

Data Definition Commands

• Create table– add a table to a database

• Drop Table– remove a table from a database

• Alter Table– add or delete column(s)