Database Programming Techniques

Database Programming Techniques

CMPS 277

Raji Ghawi

rg31@aub.edu.lb

7 April 2015

Interaction with Databases

• Interactive interface – SQL commands typed directly into a monitor

– Execute file of commands • @<filename>

• Application programs or database applications– Used as canned transactions by the end users access a

database

– May have Web interface

– Host language: Java, C/C++/C# , …

– Database language: SQL

Database Programming Approaches

• Embedded SQL Approach

– Embedded SQL ( C language)

– SQLJ (Java language)

• Library of Function Calls Approach.

– JDBC

– SQL/CLI

• Database Programming Language Approach

– Stored Procedures

Database Programming Approaches

• Embedded SQL Approach

– Embedded SQL ( C language)

– SQLJ (Java language)

• Library of Function Calls Approach.

– JDBC

– SQL/CLI

• Database Programming Language Approach

– Stored Procedures

JDBCOne API to Access Them All

Introduction

• JDBC: Java DataBase Connectivity

• JDBC is a standard interface that lets you access virtually any tabular data source from the Java programming language

– relational databases, spreadsheets, flat files

• The JDBC classes and interfaces are in the java.sqlpackage

General Architecture

Java Application or Applet

JDBC Driver Manager

Oracle Driver

MySQLDriver

PostgreSQLDriver

Oracle PostgreSQLMySQL

• The Driver Manager provides a consistent layer between your Java application and back-end database.

• Is an interpreter that translates JDBC method calls to vendor-specific database commands

• Implements interfaces in java.sql

• Can also provide a vendor’s extensions to the JDBC standard

DriverJDBC calls

Database commands

Database

A JDBC Driver

Query

Close

Connect

Process results

Overview of Querying a Database With JDBC

Register the driver

Connect to the database

Stage 1: Connect

Query

Close

Connect

Process results

1. Register the driver.

2. Connect to the database.

DriverManager.registerDriver(new org.postgresql.Driver());

Connection conn = DriverManager.getConnection

(URL, userid, password);

Connection conn = DriverManager.getConnection

("jdbc:postgresql://localhost/University",

"xxxx", "xxxx");

How to Make the Connection

Using Connection

java.sql.Connection Creating Statement

Transaction Management

Get database metadata

Conneciton related

createStatment()prepareStatment(String)prepareCall(String)

commit()rollback()

getMetaData()

close()isClosed()

List of JDBC Drivers

DBMS Driver / URL

PostgreSQLorg.postgresql.Driver

jdbc:postgresql://[host]/[DB]

MySQLcom.mysql.jdbc.Driver

jdbc:mysql://[host]/[DB]

Oracle

oracle.jdbc.driver.OracleDriver

jdbc:oracle:thin:@[host]:[port]:[db]jdbc:oracle:oci:@[host]:[port]:[db]

SQL Servercom.microsoft.sqlserver.jdbc.SQLServerDriver

jdbc:sqlserver://[host];databaseName=[db];

ODBC bridgesun.jdbc.odbc.JdbcOdbcDriver

jdbc:odbc:[db]

Demonstration

import java.sql.*;

public class MyDBApp1 {

public static void main(String[] args) {

String url = "jdbc:postgresql://localhost/University";

String username = "xxxx";

String passwd = "xxxx";

try {

Class.forName("org.postgresql.Driver");

Connection connection = DriverManager.getConnection(url, username, passwd);

// do something with connection

} catch (ClassNotFoundException e) {

e.printStackTrace();

} catch (SQLException e) {

e.printStackTrace();

}

}

}

Create a statement

Query the database

Stage 2: Query

Query

Close

Connect

Process results

The Statement Object

• A Statement object sends your SQL statement to the database.

• You need an active connection to create a JDBC statement.

• Statement has three methods to execute a SQL statement:– executeQuery() for SELECT statements– executeUpdate() for INSERT, UPDATE, DELETE, or

DDL statements– execute() for either type of statement

1. Create an empty statement object.

2. Execute the statement.

Statement stmt = conn.createStatement();

ResultSet rset = stmt.executeQuery(statement);

int count = stmt.executeUpdate(statement);

boolean isquery = stmt.execute(statement);

How to Query the Database

Statement stmt = conn.createStatement();

ResultSet rset = stmt.executeQuery

("SELECT fname, lname FROM student");

Statement stmt = conn.createStatement();

int rowcount = stmt.executeUpdate

("DELETE FROM student WHERE studid = '201231521'");

Querying the Database: Examples

• Execute a select statement.

• Execute a delete statement.

Step through the results

Assign results to Java variables

Stage 3: Process the Results

Close

Connect

Process results

Query

The ResultSet Object

• JDBC returns the results of a query in a ResultSet object.

• A ResultSet maintains a cursor pointing to its current row of data.

• Use next() to step through the result set row by row.

• getString(), getInt(), and so on assign each value to a Java variable.

1. Step through the result set.

2. Use getXXX() to get each column value.

while (rset.next()) { … }

String val =

rset.getString(colname);

while (rset.next()) {

String fname = rset.getString("fname");

String email = rset.getString("email");

// Process or display the data

}

String val =

rset.getString(colIndex);

How to Process the Results

while (rset.next()) {String email = rset.getString("email");if (rset.wasNull() {

… // Handle null value}

…}

How to Handle SQL Null Values

• Java primitive types cannot have null values.

• Do not use a primitive type when your query might return a SQL null.

• Use ResultSet.wasNull() to determine whether a column has a null value.

Mapping Database Types to Java Types

• ResultSet maps database types to Java types.

ResultSet rset = stmt.executeQuery("SELECT id, birth_date, name FROM student");

int id = rset.getInt(1);Date birthdate = rset.getDate(2); String name = rset.getString(3);

Column Name Type

id INTEGER

birthdate DATE

name VARCHAR

JDBC Type Java Type

BIT boolean

TINYINT byte

SMALLINT short

INTEGER int

BIGINT long

REAL float

FLOATDOUBLE

double

BINARYVARBINARYLONGVARBINARY

byte[]

CHARVARCHARLONGVARCHAR

String

Mapping Database Types to Java Types

JDBC Type Java Type

NUMERICDECIMAL

BigDecimal

DATE java.sql.Date

TIMETIMESTAMP

java.sql.Timestamp

CLOB Clob*

BLOB Blob*

ARRAY Array*

STRUCT Struct*

REF Ref*

JAVA_OBJECT underlying Java class

* SQL3 data type supported in JDBC 2.0

Close the result set

Close the statement

Close the connection

Stage 4: Close

Close

Connect

Query

Process Results

1. Close the ResultSet object.

2. Close the Statement object.

3. Close the connection.

rset.close();

stmt.close();

conn.close();

How to Close the Connection

Demonstration

public static void main(String[] args) {

String url = "jdbc:postgresql://localhost/University";

String username = "xxxx";

String passwd = "xxxx";

try {

Class.forName("org.postgresql.Driver");

Connection connection = DriverManager.getConnection(url, username, passwd);

Statement stmt = connection.createStatement();

String sql2 = "SELECT * FROM student";

ResultSet rs = stmt.executeQuery(sql2);

while (rs.next()) {

int id = rs.getInt("studId");

String fname = rs.getString("fname");

String lname = rs.getString("lname");

String email = rs.getString("email");

String major = rs.getString("major");

System.out.printf("%-12d %-10s %-10s %-25s %-6s \n", id, fname, lname, email, major);

}

} catch (ClassNotFoundException e) {

e.printStackTrace();

} catch (SQLException e) {

e.printStackTrace();

}

}

Demonstration

create statement object

SQL query

execute a query, returns a ResultSet object

loop over results

fetch results from ResultSet object into Java variables

format and print results

close the result set and the statement

Demonstration

Improve the structure of your program

make a global connection

move connecting code into a separate method

call your connect method from the constructor

Improve the structure of your program

separate database operations into

methods

Improve the structure of your program

call operational methods from main() as needed

Improve your program much more

• Create a pretty Graphical User Interface

– Swing: JPanel, JTable, …

• Make Java classes for your database entities

• Use suitable Design Pattern

– Singleton pattern

Improve your program much more

Improve your program much more

Security Issue

SQL Injection

Prepared Statements

• A PreparedStatement object holds precompiled SQL statements.

• Use this object for statements you want to execute more than once.

• A prepared statement can contain variables that you supply each time you execute the statement.

How to Create a Prepared Statement

1.Register the driver and create the database connection.

2.Create the prepared statement, identifying variables with a question mark (?).

PreparedStatement pstmt =conn.prepareStatement("UPDATE studentSET email = ? WHERE studID = ?");

PreparedStatement pstmt =conn.prepareStatement("SELECT deptName FROMdepartment WHERE deptCode = ?");

How to Execute a Prepared Statement

1. Supply values for the variables.

2. Execute the statement.

pstmt.setXXX(index, value);

pstmt.executeQuery();

pstmt.executeUpdate();

PreparedStatement pstmt =conn.prepareStatement("UPDATE studentSET email = ? WHERE studID = ?");

pstmt.setString(1, "abcd@gmail.com");pstmt.setInt(2, studId);pstmt.executeUpdate();

Demonstration

SQL query with placeholders

Supply values to the placeholders

Create PreparedStatement object

Execute the prepared update statement

Much more still to do

• Transaction Management

• Scrollable Result Set

• Updatable Result Set

• Callable Statements

• Metadata

– DatabaseMetaData

– ResultSetMetaData

JDBC Resources

• JDBC Tutorials

– http://www.oracle.com/technetwork/java/index-141229.html

• JDBC Online Courses

– http://www.oracle.com/technetwork/java/index-137757.html

• JDBC Books

– http://www.oracle.com/technetwork/java/index-142052.html

Database Programming Approaches

• Embedded SQL Approach

– Embedded SQL ( C language)

– SQLJ (Java language)

• Library of Function Calls Approach.

– JDBC

– SQL/CLI

• Database Programming Language Approach

– Stored Procedures

Stored Procedures

Persistent Stored Modules

Stored Procedures

Views

Way to register queries inside DBMS

Stored Procedures

Way to register code inside DBMS

Stored Procedures

• What is stored procedure?– Piece of code stored inside the DBMS

– SQL allows you to define procedures and functions and store them inside DBMS

• Advantages– Reusability: do not need to write the code again and again

– Programming language-like environment• Assignment, Loop, For, IF statements

– Call it whenever needed• From select statement, another procedure, or another function

SQL/PSM

• SQL/Persistent Stored Modules

• ISO standard defining an extension of SQL with a procedural language for use in stored procedures.

PL/SQL Transact-SQL

SQL PLMySQL

stored procedures

PL/pgSQL

Stored Procedures in PostgreSQL

• PostgreSQL allows user-defined functions to be written in other languages besides SQL and C:

– PL/pgSQL

– PL/Perl

– PL/Tcl

– PL/Python

PL/pgSQL

• PL/pgSQL: Procedural Language postgreSQL

• The design goals of PL/pgSQL were to create a procedural language that

– can be used to create functions and trigger procedures,

– adds control structures to the SQL language,

– can perform complex computations,

– inherits all user-defined types, functions, and operators,

– is easy to use.

Structure of PL/pgSQL functions

CREATE [OR REPLACE] FUNCTION <functionName> (<paramList>) RETURNS [<type> | VOID]AS $$[ DECLARE

<declarations> ]BEGIN

<functionBody>;END;$$ LANGUAGE plpgsql;

If exists, then drop it and create it again

A parameter in the paramList is specified as:<name> <mode> <type>

Mode:IN input parameter (default)OUT output parameterINOUT input and output parameter

Example 1

CREATE FUNCTION remove_emp(empID INTEGER) RETURNS void AS $$

BEGIN

DELETE FROM employee

WHERE employee.emp_id = empID ;

RETURN ;

END;

$$ LANGUAGE plpgsql;

Function name Parameter list nothing to return

RETURN means exit the function

parameter used inside SQL

SELECT remove_emp(110);

Stored procedures can be called:

• from SQL• from other functions• from applications (JDBC CallableStatement)

Declarations

• Examples

quantity INTEGER DEFAULT 32;

url VARCHAR := 'http://mysite.com';

user_id CONSTANT INTEGER := 10;

name [CONSTANT] type [NOT NULL] [{DEFAULT | := } expression];

Control Structures (Conditionals)

IF boolean-expression THENstatements

END IF;

IF-THEN

IF boolean-expression THENstatements

ELSEstatements

END IF;

IF-THEN-ELSE

IF boolean-expression THENstatements

[ ELSIF boolean-expression THENstatements

[ ELSIF boolean-expression THENstatements...]]

[ ELSEstatements ]

END IF;

IF-THEN-ELSIF

CASE search-expressionWHEN expression [, expression [ ... ]] THEN

statements[ WHEN expression [, expression [ ... ]] THEN

statements... ]

[ ELSEstatements ]

END CASE;

Simple CASE

CASEWHEN boolean-expression THEN

statements[ WHEN boolean-expression THEN

statements... ]

[ ELSEstatements ]

END CASE;

Searched CASE

Control Structures (Loops)

[ <<label>> ]

LOOP

statements

END LOOP [ label ];

LOOP

EXIT [ label ] [ WHEN boolean-expression ];

EXIT

[ <<label>> ]

WHILE boolean-expression LOOP

statements

END LOOP [ label ];

WHILE

CONTINUE [ label ] [ WHEN boolean-expression ];

CONTINUE

FOR (Integer Variant)

[ <<label>> ]

FOR name IN [ REVERSE ] expression .. expression [ BY expression ] LOOP

statements

END LOOP [ label ];

[ <<label>> ]

FOR target IN query LOOP

statements

END LOOP [ label ];

FOR (Query Results Variant)

Example 2

• Raise the salary of employees of a given department by a certain ratio.

– dept_id = 1

– ratio = 0.10

• Keep track of salary changes.

emp_id emp_name salary dept_id

101 John 1000 1

102 Jack 1100 1

103 Smith 1200 2

104 Walter 1000 2

105 Mike 1500 2

106 Sarah 1600 3

107 Judie 1250 3

emp_id change_date old_salary new_salary

Employee

Salary_History

Example 2CREATE FUNCTION raise_salary(deptID INTEGER, ratio REAL)

RETURNS void AS $$

DECLARE

oldSal REAL; newSal REAL;

curs1 CURSOR FOR

SELECT * FROM employee

WHERE employee.dept_id = deptID;

BEGIN

FOR var IN curs1 LOOP

oldSal := var.salary;

newSal := oldSal + oldSal * ratio;

UPDATE employee

SET salary = newSal

WHERE CURRENT OF curs1;

INSERT INTO salary_history

VALUES(var.emp_id, current_date, oldSal, newSal);

END LOOP;

RETURN;

END ;

$$ LANGUAGE plpgsql;

Use cursor to iterate rows

Define a cursor that references the input parameter

variable assignments

Dec

lara

tio

n

Sect

ion

update the row which the cursor is positioned on

Implicit row-variable

parameter used inside Cursor

Fun

ctio

n B

od

y

Runemp_id emp_name salary dept_id

101 John 1000 1

102 Jack 1100 1

103 Smith 1200 2

104 Walter 1000 2

105 Mike 1500 2

106 Sarah 1600 3

107 Judie 1250 3

SELECT raise_salary(1, 0.10);

emp_id change_date old_salary new_salary

emp_id emp_name salary dept_id

101 John 1100 1

102 Jack 1210 1

103 Smith 1200 2

104 Walter 1000 2

105 Mike 1500 2

106 Sarah 1600 3

107 Judie 1250 3

emp_id emp_name salary dept_id

101 John 1100 1

102 Jack 1210 1

103 Smith 1380 2

104 Walter 1150 2

105 Mike 1725 2

106 Sarah 1600 3

107 Judie 1250 3

emp_id change_date old_salary new_salary

101 2015-04-06 1000 1100

102 2015-04-06 1100 1210

emp_id change_date old_salary new_salary

101 2015-04-06 1000 1100

102 2015-04-06 1100 1210

103 2015-04-07 1200 1380

104 2015-04-07 1000 1150

105 2015-04-07 1500 1725

SELECT raise_salary(2, 0.15);

Employee Salary_History

Much more still to do

• Exception handling

• Complex data types

– Arrays, Tables

• User defined data types

– (Object-Relational Model)

• Triggers

– (Active Databases)

References

• PostgreSQL Documentation

PL/pgSQL - SQL Procedural Language

– http://www.postgresql.org/docs/8.3/static/plpgsql.html

• Fundamentals of Database Systems, Elmasri and Navathe, 6th Edition, Chapter 13

Some slides are adopted from:– www.cse.lehigh.edu/~glennb/oose/ppt/JDBC.ppt

Thank you