overview of jdbc,pro*c and oracle connectivity on omega

Overview of JDBC and Pro*C 1

Overview of JDBC,Pro*C and Oracle connectivity on Omega

CSE 5330 – Database Systems


Options for doing the project

• Windows application using Java– JDBC for database connectivity

– Java AWT / Swing etc. for the GUI

• Menu driven program using Pro*C– If you know C, but not Java


Java Database Connectivity (JDBC)

• JDBC provides a standardized library for accessing relational databases

– Connecting to the database

– Initiating queries

– Creating stored (parameterized) queries

– Data structure for the query result

• JDBC is not embedded SQL

• JDBC is located in java.sql package


JDBC driver

Java application

JDBC driver manager

JDBC API

Oracle JDBC driver(classes12.zip)

JDBC driver API

Oracle database

Client

Server (omega)


JDBC driver (continued)

• JDBC driver for Oracle needs to be on the client machine

• Available on omega at– /opt/oracle/product/9.2.0.4.0/jdbc/lib/classes12.zip

• The JDBC driver (classes12.zip) needs to be included in the runtime classpath


Six steps in using JDBC

1. Load the driver

2. Establish a connection

3. Create a statement object

4. Execute a query

5. Process the results

6. Close the connection


JDBC usage steps - details

• Step 1 : Load the drivertry

{

Class.forName ("oracle.jdbc.driver.OracleDriver");

}

catch(Exception e)

{

System.out.println("JDBC ORACLE driver failed to load");

}



• Step 2 : Establish a connection• try

• {

• con = DriverManager.getConnection("jdbc:oracle:thin:scott/[email protected]:1521:CSE1");

• }

• catch(Exception e)

• {

• System.out.println("Failed to connect to the database");

• }



• Step 3 : Create a statement– Statement statement = con.createStatement();

• Step 4 : Execute a queryString query = “SELECT FNAME, SALARY FROM EMPLOYEE”;

ResultSet rs = Statement.executeQuery(query);

• (For SELECT)

String query = “UPDATE EMPLOYEE SET SALARY = 50000 WHERE FNAME = “John”;

Statement.executeUpdate(query);

• (For UPDATE, INSERT, DELETE)



• Step 5 : Process the resultWhile (rs.next())

{

System.out.println(rs.getString(1) + “ “ + rs.getInt(2));

}

• First column has index 1, not 0

• ResultSet provides various getXXX methods that take a column index, and return the data



• Step 6 : Close the connection– con.close();

• As opening a connection is expensive, postpone this step if additional database operations are expected


Online resources

• JDBC tutorial– http://java.sun.com/docs/books/tutorial/jdbc/

• JDBC API reference– http://java.sun.com/j2se/1.4.2/docs/api/java/sql/package-summary.html


Pro*C

• Embedded SQL– Allows you to embed SQL in C code

Pro*C program C codePre-compiler

ExecutableC compiler

Embedded SQL statements SQL statements replacedBy library calls

SQLLIB

Oracle runtime library


Pro*C syntax

• SQL statements can be placed anywhere between a C block

• All SQL statements need to start with EXEC SQL and be terminated by a semicolon

{

int a;

/* ... */

EXEC SQL SELECT salary INTO :a

FROM Employee

WHERE SSN=876543210;

/* ... */

printf("The salary is %d\n", a);

/* ... */

}

• Be sure to include sqlca.h


Connecting to the database

• Legal waychar *username = "SCOTT";

char *password = "TIGER";

…

EXEC SQL CONNECT :username IDENTIFIED BY :password;

• Illegal way– EXEC SQL CONNECT SCOTT IDENTIFIED BY TIGER;

– EXEC SQL CONNECT 'SCOTT' IDENTIFIED BY 'TIGER';


Dynamic sql

• Used to dynamically create entire SQL statements

– char *s = "INSERT INTO emp VALUES(1234, 'jon', 3)";

– EXEC SQL PREPARE q FROM :s;

– EXEC SQL EXECUTE q;

• Alternately,– char *s = "INSERT INTO emp VALUES(1234, 'jon', 3)";

– EXEC SQL EXECUTE IMMEDIATE :s;


Host variables

• Key to the communication between the host program and the database

• They should be declared in a Declare section

– EXEC SQL BEGIN DECLARE SECTION;

– /* Declare all host variables inside this section:

– */ char *uid = "scott/tiger";

– ...

– EXEC SQL END DECLARE SECTION;


Transactions

• Sequence of SQL statements that are treated as a single unit of work

• Transaction ends when you issue– EXEC SQL COMMIT;


Cursors

• Used for fetching multiple rows of data

• First, declare it.– EXEC SQL DECLARE emp_cursor CURSOR FOR

– SELECT ename, empno, sal

– FROM emp

– WHERE deptno = :dept_number;

• Then, open it.– EXEC SQL OPEN emp_cursor;

• Fetch the records.– for (;;)

– {

– EXEC SQL FETCH emp_cursor INTO :emp_name1, :salary1;

– }


Cursors (continued)

• Finally, close it.– EXEC SQL CLOSE emp_cursor;

• Error handling– Every executable SQL statement returns a status code to the SQLCA variable

sqlcode

– A zero status code means that Oracle executed the statement without detecting an

error or exception – A positive status code means that Oracle executed the statement but detected an

exception – A negative status code means that Oracle did not execute the SQL statement

because of an error.


Online reference

•Pro*C/C++ Precompiler Programmer's Guide•http://omega.uta.edu/oracle/appdev.920/a97269/pc_01int.htm


Oracle connectivity on Omega

• To connect with Oracle the SSH tool may be used

• It is available for download from

http://www.uta.edu/oit/downloads.html

Once downloaded , omega can be accessed as follows:-



Once you submit this box, you will be asked to enter your password as follows :-



• Incase you reside at an off-campus location, you will not be able to directly access http://omega.uta.edu using SSH

• You will need to download and connect using a VPN client and then connect through SSH to omega.

• The VPN client can be downloaded from

http://www.uta.edu/oit/clientservices/network/vpn/pc/vpn_pc.html

overview of jdbc,pro*c and oracle connectivity on omega

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