System Aspects of SQL - inf.fu-berlin.de fileSystem Aspects of SQL SQL Environment User Access...

System Aspects of SQLSystem Aspects of SQL

SQL Environment

User Access Control

SQL in Programming Environment

Embedded SQL

SQL and Java

Transactions (Programmers View)

FU-Berlin, DBS I 2

006, H

inze / S

SQL Environment: IntroductionSQL Environment: Introduction

�SQL server � Supports operations on database elements

� Typically runs on large host machine

�SQL client� Supports user connections to server

� Runs on (different) host machine

�Connection� Channel between client and server

FU-Berlin, DBS I 2

006, H

inze / S

SQL Environment: IntroductionSQL Environment: Introduction

�Session� All SQL operations performed while connection open� Current catalog, current schema , authorized user

�Application� Module: application program� SQL agent: execution of module

SQL ClientSQL ServerConnection

Session

SQL EnvironmentSQL agent

FU-Berlin, DBS I 2

006, H

inze / S

SQL Environment: Module TypesSQL Environment: Module Types

�Generic SQL Interface:� Module: each query or statement

�Embedded SQL:� SQL statements within host-language program

� SQL statements pre-processed to function calls

� Calls executed at run-time

�True modules:� Collection of stored procedures

� Host language code, SQL code

FU-Berlin, DBS I 2

006, H

inze / S

SQL Environment: PrivilegesSQL Environment: Privileges

�User� Outside schema, handling implementation dependent

� Identification by Authorization ID (user name)

�Role� Defines user group

� Inside schema, handling via SQL statements

� Identification by Authorization ID (role name)

� All users: special role PUBLIC

� Examples:

CREATE ROLE Customer; CREATE ROLE Secretary WITH ADMIN Klaus; CREATE ROLE Movie_staff; CREATE ROLE Shop_owner;

FU-Berlin, DBS I 2

006, H

inze / S

User Access Control: IntroductionUser Access Control: Introduction

�Secrecy: � Users should not be able to see things they are not supposed to.

� e.g., A student can’t see other students’ grades.

�Integrity: � Users should not be able to modify things they are not supposed to.

� e.g., Only instructors can assign grades.

�Availability: � Users should be able to see and modify things they are allowed to.

FU-Berlin, DBS I 2

006, H

inze / S

User Access Control: IntroductionUser Access Control: Introduction

�Security policy specifies authorization�Security mechanism enforces a security policy

�Two mechanisms at DBMS level

�Discretionary access control� Concept of privileges for objects (tables and views)� Mechanisms for giving and revoking users privileges

�Mandatory access control� System-wide policies for DBS� DB object have security class� Rules on security classes govern access � Used for specialized (e.g., military) applications

FU-Berlin, DBS I 2

006, H

inze / S

User Access Control: PrivilegesUser Access Control: Privileges

�Privileges� Right to perform SQL statement type on objects

� Assigned to roles (authorization IDs)

� Creator of object: all privileges

� DBMS: management of privileges and access rights

�Privilege types:� SELECT on table or view

� INSERT on table or view

� DELETE on table or view

� UPDATE on table or view

� REFERENCES: right to refer to relation in constraint

� USAGE: (SQL-92) right to use specified domain

� ALL PRIVILEGES: short form for all privileges

FU-Berlin, DBS I 2

006, H

inze / S

�Example

�Privileges: � SELECT on Tape

� SELECT on Format

� INSERT on Format

INSERT INTO Format(name)

SELECT format

FROM Tape t

WHERE t.format NOT IN (SELECT name

FROM format);

FU-Berlin, DBS I 2

006, H

inze / S

�Grant privilege

� GRANT OPTION: Right to pass privilege on to other users

� Only owner can execute CREATE, ALTER, and DROP

GRANT <privileges> ON <object>

TO <users> [WITH GRANT OPTION]

GRANT <privileges>

ON <tablename(<attributenames>)>

TO <users> [WITH GRANT OPTION]

�Privilege to SELECT particular columns in a table

FU-Berlin, DBS I 2

006, H

inze / S

�Examples:

GRANT INSERT, SELECT ON Movie TO Klaus

Klaus can query Movie or insert tuples into it.

GRANT DELETE ON Movie TO shop_owner WITH GRANT OPTION

Anna can delete tuples, and also authorize others to do so

GRANT UPDATE (pricePDay) ON Movie TO movie_staff

Staff can update (only) the price field of Movie tuples

GRANT SELECT ON MovieView TO Customers

This does NOT allow the customers to query Movie directly!

FU-Berlin, DBS I 2

006, H

inze / S

User Access Control: Privileges on viewsUser Access Control: Privileges on views

�Creator has privilege on view if privilege on all underlying tables

�Creator loses SELECT privilege on underlying table ⇒ view is dropped

�Creator loses a privilege on underlying table ⇒creator loses privilege on view

�Creator loses a privilege held with grant option on underlying table ⇒ users who were granted that privilege on the view lose privilege on view

FU-Berlin, DBS I 2

006, H

inze / S

�Revoke privilege

� RESTRICT: only revoke if non of the privileges have been granted by these users

� Privilege given from different users – must be revoked from all users to loose privilege

REVOKE <privileges>

ON <object>

FROM <users> RESTRICT

Core SQL:1999

FU-Berlin, DBS I 2

006, H

inze / S

User Access Control: ExamplesUser Access Control: Examples

Owner: GRANT Update ON Movie TO Klaus;

Owner: GRANT Update ON Movie TO Anna;

Owner: REVOKE Update ON Movie FROM Klaus RESTRICT;

Klaus Anna

FU-Berlin, DBS I 2

006, H

inze / S

Owner: GRANT Update ON Movie TO Klaus WITH GRANT OPTION;

Klaus: GRANT Update ON Movie TO Anna;

Owner: REVOKE Update ON Movie FROM Klaus RESTRICT;

Klaus Anna

Priv Priv

Grant Command fails !

FU-Berlin, DBS I 2

006, H

inze / S

�Revoke privilege

� CASCADE: revoke from all users that have been granted the privilege by these users

� RESTRICT: only revoke if non of the privileges have been granted by this user

REVOKE [GRANT OPTION FOR] <privileges>

ON <object>

FROM <users> {RESTRICT | CASCADE}

enhanced SQL:1999

FU-Berlin, DBS I 2

006, H

inze / S

Owner: REVOKE Update ON Movie FROM Klaus CASCADE;

Klaus Anna

FU-Berlin, DBS I 2

006, H

inze / S

Owner: REVOKE GRANT OPTION FOR Update ON Movie FROM Klaus CASCADE;

Klaus Anna

FU-Berlin, DBS I 2

006, H

inze / S

Owner: REVOKE GRANT OPTION FOR Update ON Movie FROM Klaus CASCADE;

Klaus Anna

Owner: GRANT Update ON Movie TO Klaus WITH GRAND OPTION;

Owner: GRANT Update ON Movie TO Anna;

FU-Berlin, DBS I 2

006, H

inze / S

User Access Control: Object ownersUser Access Control: Object owners

�Schema owner: � Right for create, drop, alter (no privilege, not grantable)

� All privileges on schema objects

�Object creator/owner:� Create statement: current authorizationID is owner

� Enhanced SQL:1999 : owner needn't be creator

�Current user privileges in Oracle:

SQL> SELECT * FROM session_privs;

PRIVILEGE

----------------------------------------

CREATE SESSION

ALTER SESSION

CREATE TABLE

SQL> SELECT * FROM session_privs;

PRIVILEGE

----------------------------------------

CREATE SESSION

ALTER SESSION

CREATE TABLE

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: IntroductionSQL in Programs: Introduction

�SQL� Sub-language for data access

� Efficient database operations

�Host language: � Control structures

� Complex computations

� User interface: output formatting, forms

� Transactions: DB interactions as unit of work

�SQL and host language needed

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Impedance MismatchSQL in Programs: Impedance Mismatch

�Impedance Mismatch:

differing data model of SQL and host language

�Problems:� Set oriented operations vs manipulation of individuals

� Interconnection of program variables and SQL statements

� Compilation time of embedded SQL-statements

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Program/DBS CommunicationSQL in Programs: Program/DBS Communication

1. Fourth Generation Languages (4GL)� Decreasing importance

2. Module Languages� Standardized in SQL:1999

3. Call level interface� Most important approach

� Standardized in SQL:1999

4. Component architectures� Hiding the details of DB interaction

� Example: Enterprise Java Beans (EJB)

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: 1. SQL in Programs: 1. 4GL4GL

�Underlying assumption: � application programs algorithmically simple

� sophisticated output formatting needed

� difficult to switch between different DBS

�Technical concept:

�Decreasing importance

Client workstation(presentation, requests, GUI)

Database server

Proprietary protocol

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: 2. SQL in Programs: 2. ModulesModules

�Parameterized modules of SQL statements

�Standardized in SQL:1999

�Compiled for a particular language

�Linked to application program

�Language Examples: COBOL, C, ADA, ...

�Disadvantages:� SQL code hidden in application and vice versa

� Not widely used

�Used in stored procedures (e.g., Oracle PL/SQL)

�Executed under control of DBS

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: 2. SQL in Programs: 2. Modules (cont)Modules (cont)

�Example:MODULE demo NAMES are ascii

LANGUAGE FORTRAN

SCHEMA movie_db AUTHORIZATION ...

PROCEDURE discount_op

(SQLSTATE, :title VARCHAR(40),

:discount DECIMAL(3,2))

UPDATE Movie M

SET pricePday = pricePday - :discount

WHERE M.title = :title;

PROCEDURE customerState

(SQLSTATE, :customer INTEGER)

SELECT movie_id,tape_id,from_date

FROM Tape T, Rental R

WHERE R.member = customer

AND R.tape_id = T.id;

MODULE demo NAMES are ascii

LANGUAGE FORTRAN

SCHEMA movie_db AUTHORIZATION ...

PROCEDURE discount_op

(SQLSTATE, :title VARCHAR(40),

:discount DECIMAL(3,2))

UPDATE Movie M

SET pricePday = pricePday - :discount

WHERE M.title = :title;

PROCEDURE customerState

(SQLSTATE, :customer INTEGER)

SELECT movie_id,tape_id,from_date

FROM Tape T, Rental R

WHERE R.member = customer

AND R.tape_id = T.id;

ProgramLanguagevariables

Returnedstate value

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: 3. Call level interfaceSQL in Programs: 3. Call level interface

�Interface in standard programming languages

�Proprietary library routines, API

�Embedded C / Java / ..Standardized language extensions

�Standardized API � Open Database connection (ODBC),

� Java Database Connectivity (JDBC)

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: 3. Call level interfaceSQL in Programs: 3. Call level interface

�Language/DBS specific library of procedures

�Example: MySQL C API� Buffer for transferring commands and results

� API data types, e.g.,

� API functions, e.g.,

MYSQL handle for db connections

MYSQL_RES result set structure

mysql_real_query()

mysql_real_query(MYSQL *mysql,

const char *query,

unsigned int queryLength)

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Embedded SQLSQL in Programs: Embedded SQL

�Direct SQL:� SQL interpreter accepts and executes SQL commands

�SQL in host language:� Program in programming language (C, Java,…)

� Parts of program in SQL statements

� Most implementations: call level interface used

� Most popular: Embedded C (Oracle: PRO*C)

�Java support� SQLJ = Embedded Java

� JDBC = Standardized call interface for Java

FU-Berlin, DBS I 2

006, H

inze / S

�Program with "native" and SQL-like statements

�Pre-compiler = Preprocessor creates native code

�Calls to DBS resources included

�Programmer: embedded SQL or function calls

Preprocessor

Host language+

Embedded SQL

Host language+

Function CallsHost languagecompiler

Object-codeprogram

SQLlibrary

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Static/dynamic embeddingSQL in Programs: Static/dynamic embedding

�Static embedding: � SQL commands known in advance

� SQL-compilation and language binding at pre-compile time

�Dynamic SQL: � SQL-String compiled at runtime

� variable bindings at runtime

FU-Berlin, DBS I 2

006, H

inze / S

�Concepts:� Well defined type mapping (for different languages)

� Syntax for embedded SQL statements

� Binding to host language variables

� Exception handling

WHENEVER <condition> <action>SQLSTATE

EXEC SQL {SELECT title FROM ...}

EXEC SQL {SELECT id FROM Movie

WHERE titel = :titleString};...

FU-Berlin, DBS I 2

006, H

inze / S

�SQL / Host Language Interface:

� Embedded SQL-statement:

� Shared variables:

� Exception handling:

EXEC SQL <sql statement>

:<variableName> (access in SQL)

<variableName> (access in host language)

SQLSTATE (SQL function execution status)

e.g., 00000 - no problem

02000 – answer tuple not found

FU-Berlin, DBS I 2

006, H

inze / S

�Shared variable declaration

�Syntax:

� Declaration in host language

� Use variable types in common

�Example:

EXEC SQL BEGIN DECLARE SECTION;

EXEC SQL END DECLARE SECTION;

integer movie_number;integer movie_number;

integer tape_number; integer tape_number;

FU-Berlin, DBS I 2

006, H

inze / S

�Single row results: � direct insert into variable

�Syntax:

�Multiple row results:� Use of cursors on result set

EXEC SQL SELECT <attributeName>

INTO :<sharedVariable>

FROM <tableNames>

WHERE <condition>

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Cursor conceptSQL in Programs: Cursor concept

�Cursor: � Name of SQL statement and

� Handle for processing the result set record by record

�Defined at runtime

�Opened at runtime (SQL-statement executed)

�Used in most language embeddings of SQL � e.g., ESQL-C, PL/SQL, JDBC

Important concept

FU-Berlin, DBS I 2

006, H

inze / S

� No binding of result attributes to variables

� Allows traversal of result set row by row

1. Cursor declaration

2. Cursor initialisation

3. Fetch tuples

4. Close cursor

OPEN FETCH EMPTY? CLOSEDECLAREyes

FU-Berlin, DBS I 2

006, H

inze / S

�Cursor declaration:

�Cursor initialisation:

� binds input variables

� executes query

� puts first results into communication area

� positions cursor before first row of the result set

EXEC SQL DECLARE <cursorName> CURSOR

FOR <query>

EXEC SQL OPEN <cursorName>;

FU-Berlin, DBS I 2

006, H

inze / S

�Fetch tuples:

� Puts next results into communication area

� Positions cursor before before next row of the result set

� Assigns tuple to shared variables

� Sets SQLSTATE

EXEC SQL FETCH <cursorName>

INTO :<shared variable>;

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: ExampleSQL in Programs: Example

#include <stdio.h>

/* declare host variables */

char userid[12] = "ABEL/xyz";

char movie_name[10];

int movie_number;

int tape_number;

char temp[32];

void sql_error();

/* include the SQL Communication Area */

#include <sqlca.h>

#include <stdio.h>

/* declare host variables */

char userid[12] = "ABEL/xyz";

char movie_name[10];

int movie_number;

int tape_number;

char temp[32];

void sql_error();

/* include the SQL Communication Area */

#include <sqlca.h>

FU-Berlin, DBS I 2

006, H

inze / S

/* main program */

main()

{ movie_number = 200;

/* handle errors */

EXEC SQL WHENEVER SQLERROR

do sql_error("Oracle error");

/* connect to Oracle */

EXEC SQL CONNECT :userid;

printf("Connected.\n");

/* main program */

main()

{ movie_number = 200;

/* handle errors */

EXEC SQL WHENEVER SQLERROR

do sql_error("Oracle error");

/* connect to Oracle */

EXEC SQL CONNECT :userid;

printf("Connected.\n");

FU-Berlin, DBS I 2

006, H

inze / S

/* declare a cursor */

EXEC SQL DECLARE movie_cursor

CURSOR FOR

SELECT m.title

FROM movie m, tape t

WHERE t.id = :tape_number

AND t.movie_id = m.id;

/* get user data */

printf(“Tape number? ");

gets(temp);

tape_number = atoi(temp);

/* declare a cursor */

EXEC SQL DECLARE movie_cursor

CURSOR FOR

SELECT m.title

WHERE t.id = :tape_number

AND t.movie_id = m.id;

/* get user data */

printf(“Tape number? ");

gets(temp);

tape_number = atoi(temp);

FU-Berlin, DBS I 2

006, H

inze / S

/* open the cursor and

identify the result set */

EXEC SQL OPEN movie_cursor;

/* fetch and process data in a loop

exit when no more data */

EXEC SQL WHENEVER NOT FOUND DO break;

while (1){

EXEC SQL FETCH movie_cursor

INTO :movie_name; …

/* open the cursor and

identify the result set */

EXEC SQL OPEN movie_cursor;

/* fetch and process data in a loop

exit when no more data */

EXEC SQL WHENEVER NOT FOUND DO break;

while (1){

EXEC SQL FETCH movie_cursor

INTO :movie_name; …

FU-Berlin, DBS I 2

006, H

inze / S

/* close cursor before another SQL

statement is executed */

EXEC SQL CLOSE movie_cursor;

EXEC SQL COMMIT WORK RELEASE;

exit(0);

/* close cursor before another SQL

statement is executed */

EXEC SQL CLOSE movie_cursor;

EXEC SQL COMMIT WORK RELEASE;

exit(0);

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Positioned UpdateSQL in Programs: Positioned Update

�Step through set of rows and update or delete

�Syntax:

�Example:

EXEC SQL DECLARE <cursorName> CURSOR

FOR <query>

FOR UPDATE ON <attribute>;

… WHERE CURRENT OF <cursorName>…

EXEC SQL DECLARE myCurs CURSOR

FOR SELECT id,length,title FROM MovieFOR UPDATE ON length

EXEC SQL UPDATE Movie

SET lenght = length + 1

WHERE CURRENT OF myCurs;

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Cursor OptionsSQL in Programs: Cursor Options

�Ordering tuples� Use ORDER BY in query

�Cursor motion � SCROLL CURSOR

� Relative to current position: PRIOR/NEXT/RELATIVE<nr>

e.g., FETCH <cursorName> PRIOR INTO ...

� Absolute position: first/last/ABSOLUTE<nr>

�Limit effect of changes� Performance: cursor FOR READ ONLY

� Concurrent access: INSENSITIVE CURSOR FOR …

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Cursor sensitivitySQL in Programs: Cursor sensitivity

�Example:

�Changes not visible in result set

�Visible if cursor closed and reopened

EXEC SQL DECLARE myCurs INSENSITIVE CURSOR

FOR SELECT id,length,title FROM MovieFOR UPDATE ON length WHERE id >100;

EXEC SQL OPEN...

EXEC SQL FETCH myCurs INTO .....

UPDATE Movie SET lenght = length + 20

WHERE CURRENT OF myCurs;

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Dynamic SQLSQL in Programs: Dynamic SQL

�Statements not known at compile time� Statements computed by host language

� User input of query

�Tasks at run-time:� Pass query string to SQL system

� Translate to executable statement

� Execute statement

�Use ‘Prepared Statements’

FU-Berlin, DBS I 2

006, H

inze / S

�Step 1:

� String: SQL statement

� SQLvariable: assigned SQL statement

� Parse and prepare statement for execution

EXEC SQL PREPARE <SQLvariable>

FROM <string>

EXEC SQL EXECUTE <SQLvariable>

�Step 2:

� Execute statement SQLvariable

FU-Berlin, DBS I 2

006, H

inze / S

�Example:

void readQuery(){

char *query;

/* prompt user for query

allocate space

make :query point to query*/

EXEC SQL PREPARE SQLquery FROM :query;

EXEC SQL EXECUTE SQLquery;

void readQuery(){

char *query;

/* prompt user for query

allocate space

make :query point to query*/

EXEC SQL PREPARE SQLquery FROM :query;

EXEC SQL EXECUTE SQLquery;

FU-Berlin, DBS I 2

006, H

inze / S

�Multiple execution:� Prepare once

� Execute many times

�Single execution:� Combination of step 1 an 2

� Example:

EXEC SQL EXECUTE IMMEDIATE <string>

EXEC SQL EXECUTE IMMEDIATE :query;

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: SQL in Programs: SQL & JavaSQL & Java

�SQLJ � Embedded SQL for Java

� Compiles to JDBC method call

� Defined and implemented by major DBS companies (Oracle in particular)

�JDBC � Java call-level interface (API) for SQL DBS

� DB vendor independent

� Supports static and dynamic SQL

� Implemented by nearly all DB vendors

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: SQLJSQL in Programs: SQLJ

�Part 1: SQLJ Embedded SQL� Mostly reviewed and implemented

� Integrated with JDBC API

� Oracle has placed Translator source into public domain

�Part 2: SQLJ Stored Procedures and UDFs� Using Java static methods as SQL stored procedures & functions

� Leverages JDBC API

�Part 3: SQLJ Data Types� Pure Java Classes as SQL ADTs

� Alternative to SQL:1999 Abstract Data Types

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: SQLJ ExampleSQL in Programs: SQLJ Example

// Part of a SQLJ program, one method:

public void changeMovie(int movieid, int newTape)

string mtitle;

int tnumber;

#sql { SELECT m.title, count(t.id)

INTO :mtitle, :tnumber

WHERE m.id = :movieid

AND m.id = t.movie_id };

if (tnumber < 3)

#sql {INSERT INTO tape VALUES

(:newTape, 'DVD', :movieid)};

// Part of a SQLJ program, one method:

public void changeMovie(int movieid, int newTape)

string mtitle;

int tnumber;

#sql { SELECT m.title, count(t.id)

INTO :mtitle, :tnumber

WHERE m.id = :movieid

AND m.id = t.movie_id };

if (tnumber < 3)

#sql {INSERT INTO tape VALUES

(:newTape, 'DVD', :movieid)};

FU-Berlin, DBS I 2

006, H

inze / S

�Java in Web context (2 tier architecture):

Java application

Business Logic (application)

Proprietary protocol of DBMS

Database Server

FU-Berlin, DBS I 2

006, H

inze / S

�Java in Web context (3 tier architecture):

Application server

Java applet or WWW Browser

Proprietary protocol of DBMS

Database Server

Business Logic (application)

HTTP, RMI, CORBA,…

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: SQL in Programs: JDBCJDBC

1. Preparation

2. Load a driver � many vendor products

� url JDBC-Driver and host information

Class.forName(

"oracle.jdbc.driver.OracleDriver");

String url = "jdbc:oracle:thin:

@<host>:<port>:<db>";

import java.sql.*;

FU-Berlin, DBS I 2

006, H

inze / S

3. Set up connection database(s)

� Several connections at a time possible

4. Create statement object

� Similar to channel for sending queries to database

Connection con = DriverManager.getConnection(

"jdbc:oracle:thin:@<host>:<port>:<db>",

<username>,<password>);

Statement stmt = con.createStatement();

FU-Berlin, DBS I 2

006, H

inze / S

5. Send SQL query string

� results in ResultSet object

6. Process results one after the other� processed with "hidden cursor"

ResultSet rs = stmt.executeQuery(“<query>" );

while (rs.next()){

for (i = 1; i <= numCols; i++){

if (i > 1) System.out.print(",");

System.out.print(rs.getString(i));

FU-Berlin, DBS I 2

006, H

inze / S

#import java.io.*;#import java.sql.*;#import java.util.*;...

SQL in Programs: JDBC ExampleSQL in Programs: JDBC Example

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

String url = "jdbc:oracle:thin:@kuh:1521:INTROKUH";

Connection con = DriverManager.getConnection

( url, “user", “passwort");

Protocol Oracle-spec. Sub-protocol Host Port

3. Connect to database

2. Load driver

1. Preparation

FU-Berlin, DBS I 2

006, H

inze / S

Statement stmt = con.createStatement();

ResultSet rs = stmt.executeQuery("SELECT id, title FROM movie");

while (rs.next()) {String n = rs.getInt(“id");String n = rs.getString(“title");System.out.println(s + ": " + n);}

5. execute statement

4. Create SQL-statement

SQL in Programs: JDBC ExampleSQL in Programs: JDBC Example

6. Process results

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: JDBC variable binding SQL in Programs: JDBC variable binding

�No explicit cursor

�Several methods in JDBC� e.g.,

�Access result data by position or by name� By position:

� By name:

boolean next(), void close(),

<JavaType> get<JavaType>(),

boolean wasNull()

String s = rs.getString(2);

String rs.getString ("b") ;

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: JDBC variable binding SQL in Programs: JDBC variable binding

�Example:

java.sql.Statement stmt = con.createStatement();

ResultSet rs1 = stmt.executeQuery

("SELECT id, title FROM movie");

while (rs1.next()) {

int mid = rs1.getInt(“id");

String mt = rs1.getString(“title");

System.out.println("ROW:" + mid + " " + mt);}

("SELECT id, movie_id FROM tape");

int tid = rs2.getInt(1);

int tmid = rs2.getInt(2);

System.out.println("ROW:" + tid + " " + tmid);}

java.sql.Statement stmt = con.createStatement();

("SELECT id, title FROM movie");

int mid = rs1.getInt(“id");

String mt = rs1.getString(“title");

System.out.println("ROW:" + mid + " " + mt);}

("SELECT id, movie_id FROM tape");

int tid = rs2.getInt(1);

int tmid = rs2.getInt(2);

System.out.println("ROW:" + tid + " " + tmid);}

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Prepared statementsSQL in Programs: Prepared statements

�Pass input parameters

�Use prepared statement

� Statement compiled

� Missing values in query: “?”

�Set value:

java.sql.PreparedStatement prepStmt =

con.prepareStatement(<query>);

prepStmt.setString(<position>, <value>);

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Prepared statementsSQL in Programs: Prepared statements

String mTitle;

con.prepareStatement(

"SELECT count(*)

FROM Movie m, Tape t

WHERE t.movie_id = m.id

AND m.title = ? );

prepStmt.setString(1, mTitle);

ResultSet rs = prepStmt.executeQuery() ;

while (rs.next()){

int i = r.getInt(1);

// by position, no name available

System.out.println("Number of tapes for " +

mTitle + " is: " +i)

String mTitle;

con.prepareStatement(

"SELECT count(*)

FROM Movie m, Tape t

WHERE t.movie_id = m.id

AND m.title = ? );

prepStmt.setString(1, mTitle);

ResultSet rs = prepStmt.executeQuery() ;

while (rs.next()){

int i = r.getInt(1);

// by position, no name available

System.out.println("Number of tapes for " +

mTitle + " is: " +i)

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Positioned updateSQL in Programs: Positioned update

�Positioned update needs cursor name

�Define cursor (JDBC 1)

� Use for updates and deletes

�Define cursor (JDBC2)� more flexible (anonymous) cursor handling

� setCursorName not implemented in Oracle Driver

public void setCursorName(String name)

throws SQLException

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Positioned updateSQL in Programs: Positioned update

�JDBC 2.0� Result set scrollable and updateable

� Example:

Statement stmt = con.createStatement(

ResultSet.TYPE_SCROLL_SENSITIVE,

ResultSet.CONCUR_UPDATABLE);

stmt.setFetchSize(25);

ResultSet rs = stmt.executeQuery(

"SELECT id, title

FROM movie");

rs.first();

rs.updateString(“title“, “xxxxx”);

rs.updateRow();

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: TransactionsSQL in Programs: Transactions

�Transaction: � Collection of one or more database operations executed atomically (either all operations or none )

�Programmers view:� Everything between beginning of a sequence of operations on the database and ‘COMMIT’ or ‘ROLLBACK’

� No explicit "transaction begin" command

... OPEN MyCurs;........ ; COMMIT;

Begin of first transaction(first SQL command in program) End of first transaction

FU-Berlin, DBS I 2

006, H

inze / S

�COMMIT� Effects on database made permanent

�ROLLBACK� Aborts transaction

� All changes in transaction undone (rolled back)

�Programmers View:� Auto-commit mode: each SQL-command is a transaction

� Various transaction isolation levels

FU-Berlin, DBS I 2

006, H

inze / S

�Transaction manager: � Isolate concurrent users from each other

�Problems:� Lost update: same object concurrently updated by two users, one update lost

� Dirty read: object value changed by transaction which aborts later

� Non-repeatable read: same object has different value within same transaction

� Phantom tuples: non-repeatable read caused by insertions or deletions

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Isolation levelsSQL in Programs: Isolation levels

�READ UNCOMMITTED

� Allows read access to uncommitted transactions

� Transaction has to be read only

� Lowest locking overhead

� Unpleasant effects may occur

�Example:� TA1 increases the prices of some movies in DB by 5%

� TA2 scrolls through all movies, sees new prices

SET TRANSACTION

READ ONLY,

ISOLATION LEVEL READ UNCOMMITTED

FU-Berlin, DBS I 2

006, H

inze / S

�READ COMMITTED

� Allows read access to committed transactions only

� Long write locks, no or short read locks

� Non-repeatable reads

�Example:

SET TRANSACTION

ISOLATION LEVEL READ COMMITTED

Read(a)

y:=y-a

Write a=a-10

commit

Wrong balance

FU-Berlin, DBS I 2

006, H

inze / S

�REPEATABLE READ

� All data isolated from concurrent writes

� Read and write locks long term until end of TA

� Phantom tuples may occur

SET TRANSACTION

ISOLATION LEVEL REPEATABLE READ

FU-Berlin, DBS I 2

006, H

inze / S

�SERIALIZABLE

� All data isolated from concurrent writes

� No phantom tuples inserted into the read set by other transaction

� Standard default

SET TRANSACTION

ISOLATION LEVEL SERIALIZABLE

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Transactions and JDBCSQL in Programs: Transactions and JDBC

�Transactional properties of connections� TRANSACTION_NONE (not implemented)

� TRANSACTION_READ_UNCOMMITTED

� TRANSACTION_READ_COMMITTED

� TRANSACTION_REPEATABLE_READ

� TRANSACTION_SERIALIZABLE

�Methods:� public void setTransactionIsolation(int

level) throws SQLExceptionpublic void

� setAutoCommit(boolean autoCommit)

� public void commit() throws SQLException

� public void rollback() throws SQLException

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Visibility of changesSQL in Programs: Visibility of changes

�Scroll-insensitive result set� no change by other result sets – even in the same TA – are visible

� Updates in result set r visible for operations on r

� Deletes / inserts (!) in result set r not visible

�Sensitive result set: � depending on connection isolation level

ResultSet rs = stmt1.executeQuery(

"SELECT id, length FROM movie");

int i = stmt2.executeUpdate (

“DELETE FROM movie“);

rs.first();

rs.updateString(“title“, “xxxxx”);

rs.updateRow();

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: Exception handlingSQL in Programs: Exception handling

�Abort transaction when error:

� WHENEVER SQLERROR CONTINUE prevents ROLLBACK from (infinite) invocation of routine

�Example:

EXEC SQL WHENEVER SQLERROR CONTINUE;

EXEC SQL ROLLBACK WORK RELEASE;

void sql_error(msg){

char buf[500];

int buflen, msglen;

buflen = sizeof (buf);

sqlglm(buf, &buflen, &msglen);

printf("%s\n", msg);

printf("%*.s\n", msglen, buf);

exit(1); }

void sql_error(msg){

char buf[500];

int buflen, msglen;

buflen = sizeof (buf);

sqlglm(buf, &buflen, &msglen);

printf("%s\n", msg);

printf("%*.s\n", msglen, buf);

exit(1); }

FU-Berlin, DBS I 2

006, H

inze / S

SQL in Programs: SummarySQL in Programs: Summary

� Access Rights� Means to ensure data security

� Privileges to roles

� Program – DB communication:� Fourth Generation Languages (4GL)

� Module Languages

� Call level interface

� Component architectures

� Transactions in programs � Isolation levels

� Begin, end transaction

System Aspects of SQL - inf.fu-berlin.de fileSystem Aspects of SQL SQL Environment User Access...

Documents

SQL T-SQL GIT Share SQL GIT Share SQL DacPacT-SQL

MY SQL SQL PL/SQL

PL/SQL (Embedded SQL)

A Detailed Survey on Various Aspects of SQL Injection in

The father of computing history: Charles Babbage by Anja Jentzsch jentzsch@inf.fu-berlin.de

Sql no sql

“Explaining EXPLAIN“ · SKIP Introduction: The “SQL“ Standard Structured [English] Query Language Does not cover all behavioral aspects – Indexes – Algorithms – Caching

Introduction to SQL. SQL What is SQL SQL Components Syntax & Conventions SQL Data Types INNER JOIN SELECT Statements

SQL Server Storage Engine. Software architect at Red Gate Software Responsible for SQL tools: ◦ SQL Compare, SQL Data Compare, SQL Packager ◦ SQL

Seminar: "Einführung in C/C++" Einführung in die Programmiersprache C/C++ Dienstag Andreas Döring doering@inf.fu-berlin.de SS 2004

We Practice What We Teach. Public Web Site Outages Web Servers SQL Server SQL Server SQL Server SQL Server SQL Server SQL Server SQL Server SQL Server

PL/SQL PL/SQL stands for Procedural Language/SQL. PL/SQL extends SQL by adding constructs found…

Microsoft SQL Server 2005. Versioni di Microsoft SQL Server 2005 SQL Server EXPRESS Edition SQL Server MOBILE Edition SQL Server WORGROUP Edition SQL

14 quasi experiment.ppt - inf.fu-berlin.de · Lutz Prechelt, prechelt@inf.fu-berlin.de 2/ 30 "Empirische Bewertung in der Informatik" Prof. Dr. Lutz Prechelt Freie Universität Berlin,

DBI319. Demo SQL Server 2005 SP2 SQL Server 2008 SQL Server 2000 SP4 SQL Server 2008 R2 SQL Server 2008 SP2 SQL Server 2008 R2 SQL

System Aspects of SQL 2

1 Chapter 7 System Aspects of SQL uSQL in a Programming Environment uTransactions uAuthorization

Surveys - inf.fu-berlin.de · Lutz Prechelt, prechelt@inf.fu-berlin.de 9 / 35 Question 4 • How much influence has learning the material had on your thinking (i.e. your approach

SQL & ADVANCED SQL

Sql y no sql