Database Systems - Application Development

Application DevelopmentSQL

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Database SystemsApplication Development

H. Turgut Uyar Sule Oguducu

2002-2014

H. Turgut Uyar, Sule Oguducu Database Systems


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License

c© 2002-2014 T. Uyar, S. OguducuYou are free to:

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Topics

1 Application DevelopmentIntroductionEmbedded SQLODBCJDBC

2 SQLStored ProceduresViewsIndexes



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IntroductionEmbedded SQLODBCJDBC

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Introduction

using the database language in conjunctionwith a general-purpose programming language

general-purpose language: host language

mismatch between SQL and the host language:

sets in SQLobjects and iteration constructs in the host language



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Program Structure

connect

server, database, username, password

run statements as needed:

query operations return result sets → iterate over rowsupdate operations return number of affected rows

disconnect



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Approaches

application programming interface (API)

embedded SQL

ODBC

language standard interfaces



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Application Programming Interface

using the library functions of the SQL server

pros: fast

cons: specific to SQL product



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API Example: PostgreSQL - C

#include <libpq-fe.h>

int main(int argc, char *argv[]){

/* connect *//* execute query *//* disconnect */

}



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API Example: Connection

/* PGconn *conn; */conn = PQconnectdb("host=localhost dbname=imdb"

" user=itucs password=itucs");if (PQstatus(conn) == CONNECTION_BAD){

fprintf(stderr, "Connection failed.\n");exit(1);

}

/* execute query */

PQfinish(conn);



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API Example: Query Execution

sprintf(query, "SELECT TITLE, SCORE"" FROM MOVIE WHERE (YR = %d)", year);

/* PGresult *result; */result = PQexec(conn, query);if (PQresultStatus(result) != PGRES_TUPLES_OK){

fprintf(stderr, "Query failed.\n");PQclear(result);PQfinish(conn);exit(1);

}



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API Example: Result Set

for (i = 0; i < PQntuples(result); i++){

title = PQgetvalue(result, i, 0);score = PQgetvalue(result, i, 1);...

}

PQclear(result);



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Embedded SQL

mark SQL statements within host language code: EXEC SQL

preprocessor: embedded SQL directives → API calls

pros: fast, standard

cons: difficult, does not support most languages



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Embedded SQL

skip Embedded SQL



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Embedded SQL

variable sharing

EXEC SQL BEGIN DECLARE SECTION;-- shared variablesEXEC SQL END DECLARE SECTION;

error control

EXEC SQL WHENEVER{ SQLERROR | SQLWARNING | NOT FOUND }{ STOP | CONTINUE | DO command | GOTO label }



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Query Results

cursors for iterating over query results

EXEC SQL DECLARE cursor_name CURSOR FORSELECT ...;

EXEC SQL OPEN cursor_name;EXEC SQL FETCH IN cursor_name INTO variables;EXEC SQL CLOSE cursor_name;

query is executed when cursor is opened



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Embedded SQL Example: Connect

EXEC SQL BEGIN DECLARE SECTION;int year;char *title = NULL, *score = NULL;EXEC SQL END DECLARE SECTION;

EXEC SQL CONNECT TO imdbUSER itucs IDENTIFIED BY itucs;

/* process query */

EXEC SQL DISCONNECT;



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Embedded SQL Example: Cursor

scanf("%d", &year);EXEC SQL DECLARE c_query CURSOR FOR

SELECT TITLE, SCORE FROM MOVIEWHERE (YR = :year);

EXEC SQL OPEN c_query;

/* execute query */

EXEC SQL CLOSE c_query;EXEC SQL COMMIT;



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Embedded SQL Example: Query

EXEC SQL WHENEVER NOT FOUND DO break;while (1){

EXEC SQL FETCH c_query INTO :title, :score;...

}



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ODBC

ODBC: Open DataBase Connectivitya service layer between the application and the server

pros: standard

cons: slow



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ODBC Architecture

application

driver manager

registers the ODBC driverstransfers requests from application to driver

driver

translates and transfers requests to data source

data source

processes instructions from the driver



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ODBC Example: PHP

$conn = odbc_connect("imdb", "itucs", "itucs");$query = "SELECT TITLE, SCORE FROM MOVIE"

. " WHERE (YR = " . $year . ")";$result = odbc_exec($conn, $query);

/* process the result set */

odbc_close($conn);



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ODBC Example: PHP

echo "<table>\n";while (odbc_fetch_row($result)) {

$title = odbc_result($result, "title");$score = odbc_result($result, "score");echo "<tr>\n";echo " <td>$title</td>\n";echo " <td>$score</td>\n";echo "</tr>\n";

}echo "</table>\n";



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JDBC

JDBC: Java DataBase Connectivity

same architectural concepts as in ODBC



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JDBC Drivers

Type I: bridges

translate into non-native calls (for example ODBC)

Type II: direct translation via non-Java driver

translate into API of data source (for example C++)

Type III: network bridges

connect to middleware serverfor translating into API of data source

Type IV: direct translation via Java driver

communicate with DBMS through Java sockets



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JDBC Flow

get a connection object:Connection conn = DriverManager.getConnection();

create a statement object on the connectionStatement stmt = conn.createStatement();

execute the query

select: ResultSet results = stmt.executeQuery(query);insert, update, delete: stmt.executeUpdate(query);

process the results

close resources which are no longer needed(result sets, statements, connections)



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Processing Results

ResultSet is an iterator

whether there are more rows: .hasNext()proceed to the next row: .next()

convert and transfer data in the row to variables

by column name: .getXXX(name)by column order: .getXXX(order)



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Data Type Conversions

SQL type Java class ResultSet method

BIT Boolean .getBoolean()CHAR String .getString()VARCHAR String .getString()FLOAT Float .getDouble()INTEGER Integer .getInt()DATE java.sql.Date .getDate()TIME java.sql.Time .getTime()TIMESTAMP java.sql.TimeStamp .getTimestamp()



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JDBC Example: Driver

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

} catch (ClassNotFoundException e) {// PostgreSQL driver not installed

}



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JDBC Example: Connect

try {conn = DriverManager.getConnection(

"jdbc:postgresql:imdb", "itucs", "itucs");

} catch (SQLException e) {// connection error

}



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JDBC Example: Insert

query = "INSERT INTO MOVIE (TITLE, YR)"+ " VALUES (’Casablanca’, 1942)";

stmt = conn.createStatement();stmt.executeUpdate(query);stmt.close();



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Security

don’t trust inputs from outside sources

Example

name = ...; // get from outside sourcequery = "INSERT INTO Students (NAME)"

+ " VALUES (’" + name + "’)";stmt = conn.createStatement();stmt.executeUpdate(query);stmt.close();



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Little Bobby Tables

http://xkcd.com/327/


http://xkcd.com/327/


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Prepared Statements

prepared statements can be reused by changing parameter values

creating:PreparedStatement stmt = conn.prepareStatement(query);

placeholder for parameters in query: ?

values must be set before executing:stmt.setXXX(order, value);

executing:ResultSet results = stmt.executeQuery();stmt.executeUpdate();



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JDBC Example: Prepared Statement

query = "INSERT INTO MOVIE (TITLE, YR) VALUES (?, ?)";stmt = conn.prepareStatement(query);for (Movie movie : getMovies()) {

stmt.setString(1, movie.getTitle());stmt.setInt(2, movie.getYear());stmt.executeUpdate();

}stmt.close();



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JDBC Example: Result Set

query = String.format("SELECT TITLE FROM MOVIE WHERE (YR = %d)", year

);stmt = conn.createStatement();results = stmt.executeQuery(query);while (results.next()) {

title = results.getString("TITLE");System.out.println("Title: " + title),

}results.close();stmt.close();



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JDBC Example: Delete

query = "DELETE FROM MOVIE WHERE (ID = ?)";stmt = conn.prepareStatement(query);stmt.setInt(1, movie.getId());stmt.executeUpdate();stmt.close();



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JDBC Example: Update

query = "UPDATE MOVIE SET YR = ? WHERE (ID = ?)";stmt = conn.prepareStatement(query);stmt.setInt(1, movie.getYear());stmt.setInt(2, movie.getId());stmt.executeUpdate();stmt.close();



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JDBC Example: Close Resources

Statement stmt = ...;ResultSet results = ...;try {

results = stmt.executeQuery(query);...

} catch (SQLException e) {...

} finally {results.close();stmt.close();

}



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Auto-Generated Identity Values

query = "INSERT INTO ... ";stmt = conn.prepareStatement(query,

Statement.RETURN_GENERATED_KEYS);stmt.executeUpdate();

ResultSet ids = stmt.getGeneratedKeys();// assuming there is one and only one resultids.next();int id = ids.getInt(1);



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Stored ProceduresViewsIndexes

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Stored Procedures

implementing functionality in the database server

languages: SQL, PL/SQL, C, ...

not portable

not scalable

database servers are not optimized for business logic

not recommended→ implement business logic on the application server



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Functions

creating a function

CREATE FUNCTIONfunction_name(parameter_type [, ...])RETURNS return_typeAS function_bodyLANGUAGE language_name

first parameter $1, second parameter $2, ...



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SQL Function Example

calculating new score:$1: old score, $2: old votes, $3: new vote

CREATE FUNCTION NEW_SCORE(float, int, int)RETURNS floatAS ’SELECT ($1 * $2 + $3) / ($2 + 1);’LANGUAGE ’sql’



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Triggers

trigger: a function that will be automatically invoked on an event

can be useful for maintaining integrity

creating a trigger:

CREATE TRIGGER trigger_name{ BEFORE | AFTER } { event [ OR ... ] }ON table_name[ FOR [ EACH ] { ROW | STATEMENT } ]EXECUTE PROCEDURE function_name(...)

PL/pgSQL:

old: tuple before the operationnew: tuple after the operation



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Trigger Example

let SCORE * VOTES be kept in the POINTS column

CREATE FUNCTION UPDATE_MOVIE_POINTS()RETURNS opaqueAS ’BEGIN

new.POINTS = new.SCORE * new.VOTES;RETURN new;END;’

LANGUAGE ’plpgsql’



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Trigger Example

calculate POINTS automatically on updates

CREATE TRIGGER UPDATE_MOVIEBEFORE INSERT OR UPDATE ON MOVIEFOR EACH ROWEXECUTE PROCEDURE UPDATE_MOVIE_POINTS()



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Views

presenting a derived table like a base table: view

isolating users and application programsfrom changes in database structure

creating a view:

CREATE VIEW view_name ASSELECT ...

SELECT will be executed every time the view is used



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View Example

identifiers, titles and years of new movies

CREATE VIEW NEW_MOVIE ASSELECT ID, TITLE, YR FROM MOVIEWHERE (YR > 1995)

SELECT * FROM NEW_MOVIE



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Updating Views

any change will have to performed on the base tables

rules need to be defined

creating a rule:

CREATE RULE rule_name ASON event TO view_name[ WHERE condition ]DO [ INSTEAD ] sql_statement



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View Rule Example

modify the title of a new movie

UPDATE NEW_MOVIE SET TITLE = ...WHERE (ID = ...)

rule for updating the base table

CREATE RULE UPDATE_TITLE ASON UPDATE TO NEW_MOVIEDO INSTEADUPDATE MOVIE SET TITLE = new.TITLEWHERE (ID = old.ID)



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Indexes

some operations require sorting:ORDER BY, DISTINCT, GROUP BY, UNION, ...

indexes speed up queries

slow down inserts and updates

creating an index

CREATE [ UNIQUE ] INDEX index_nameON table_name(column_name [, ...])



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References

Required Reading: Date

Chapter 4: An Introduction to SQL

4.6. Embedded SQL

Chapter 9: Integrity

9.11. Triggers (a Digression)

Chapter 10: Views

Supplementary Reference: Ramakrishnan, Gehrke

Chapter 6: Database Application Development


Database Systems - Application Development

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