Advanced SQL - Lecture 6 - Introduction to Databases (1007156ANR)

2 December 2005
Introduction to Databases
Advanced SQL
Prof. Beat Signer
Department of Computer Science
Vrije Universiteit Brussel
http://www.beatsigner.com

Beat Signer - Department of Computer Science - bsigner@vub.ac.be 2March 24, 2017
Context of Today's Lecture
Access
Methods
System
Buffers
Authorisation
Control
Integrity
Checker
Command
Processor
Program
Object Code
DDL
Compiler
File
Manager
Buffer
Manager
Recovery
Manager
Scheduler
Query
Optimiser
Transaction
Manager
Query
Compiler
Queries
Catalogue
Manager
DML
Preprocessor
Database
Schema
Application
Programs
Database
Manager
Data
Manager
DBMS
Programmers Users DB Admins
Based on 'Components of a DBMS', Database Systems,
T. Connolly and C. Begg, Addison-Wesley 2010
Data, Indices and
System Catalogue

Authorisation
 Different types of authorisations (privileges) can
be assigned to a user via DDL
 insert, read, update and delete privileges
 The creator of a new relation is automatically given all
privileges on that relation
grantPrivilege = "GRANT" , "ALL PRIVILEGES" , "TO" , ( "PUBLIC" |
grantee ) | "GRANT" , privilege , { "," , privilege } ) , "ON" ,
( table | view ) , { "," , ( table | view ) } , "TO" ,
( "PUBLIC" | grantee ) , [ "WITH GRANT OPTION" ];
privilege = "INSERT" | "SELECT" | ( "UPDATE" , [ "(" , column ,
{ "," , column } , ")" ] ) | "DELETE";
grantee = ( user | role ) , { "," , ( user | role ) };

Authorisation ...
 An update privilege may be limited to certain
attributes only
 Roles can be used to group users
GRANT ALL PRIVILEGES TO Alice, Bob;
GRANT INSERT, UPDATE (amount, status) ON Order TO Eve WITH GRANT OPTION;
createRole = "CREATE ROLE" , role;
grantRole = "GRANT" , role , "TO"
( "PUBLIC" | grantee );
CREATE ROLE PowerUser;
GRANT PowerUser TO Alice, Bob;

Authorisation ...
 Privileges can be passed to other users if the
WITH GRANT OPTION has been specified
 Privileges and roles can be removed via the REVOKE
command (similar to GRANT statement)
 Examples
 Note that the revocation of a privilege may have an effect
on grants that have been passed to other users
 authorisation graph has to be inspected
REVOKE INSERT ON Order FROM Eve;
REVOKE PowerUser FROM Bob;

Authorisation Graph
 Privilege revocation examples
 remove privilege from user1 (g1)  user4 still has privilege via g24
 remove privilege from user2 (g2) and user3 (g3)
- g23 still exists but is no longer part of a path starting from the admin
 user2 and user3 no longer have privilege  user5 no longer has privilege
user1
user2
user3
user4
user5admin
g1
g2
g24
g3
g14
g25
g23

Working with SQL
 There are two main modes to work with SQL
 via generic query interfaces or SQL application interfaces
 note that standard SQL is not Turing complete
 Generic SQL interface
 command-line or web-based interface
 answer single questions (one query)
 interactive query evaluation
 SQL interface for applications
 sequence of queries, inserts, updates and deletes
 SQL statements that are embedded within a host language
 query results are processed and reused in non-declarative actions
- I/O interfaces
- human-computer interaction

Impedance Mismatch Problem
 Combination of SQL with a host language
 mix of declarative and procedural programming paradigms
 two completely different data models
- relational model with sets and bags
- no pointers, loops and branches in basic SQL
- no NULL values in typical host languages
 different set of data types
- many programming languages do not offer Date or Time data types
 Interfacing with SQL is not straightforward
 data has to be converted between the host language and SQL
due to the impedance mismatch
 ~30% of the code and effort is used for this conversion!
 various libraries to simplify the mapping (e.g. Hibernate)

Impedance Mismatch Problem ...
 Why not simply use a single language?
 both languages have their domain-specific strengths
/**
* Transforms the Swiss Projection
* coordinates (y, x, h') to the
* ellipsoidic WGS84 coordinates (phi,
* lambda, h) using and approach of
* [U. Marti] based on the formulas of
* [Bolliger, 1967].
* @param swissCoordinates the Swiss
* coordinates to be transformed.
* @return the WGS84 coordinates for
* the specified Swiss coordinates.
*/
public static final WGS84Coordinates
transformSwissCoordinatesToWGS84(
SwissCoordinates swissCoordinates) {
double yPrime =
(swissCoordinates.getY() - 600000) /
1000000;
double xPrime =
(swissCoordinates.getX() - 200000) /
1000000;
double xPrimePow2 = xPrime * xPrime;
double xPrimePow3 = xPrimePow2 *
xPrime;
double yPrimePow2 = yPrime * yPrime;
double yPrimePow3 = yPrimePow2 *
...
Impedance
Mismatch
Application Code Database

SQL Programming Environments
 Embedded SQL (ESQL)
 integration of SQL in a host programming language
 e.g. interfacing with C through ESQL/C
 SQL Call-Level Interface (SQL/CLI)
 e.g. interfacing with Java through JDBC
 SQL Persistent Stored Modules (SQL/PSM)
 stored procedures
 Triggers

Database Applications
 Task sharing between client and server
 client does data presentation
 server does data management
 Where should we implement the application logic?
 on the client
- ESQL, SQL/CLI, ODBC, JDBC, ...
 on the server
- SQL/PSM, Stored Procedures, Triggers
 thin client vs. thick client

Example Database
customerID
name
street
postcode
city
orderID
customerID
cdID
date
amount
status
Customer
CDOrder
name
address
Producer
cdID
title
duration
price
year
producer
CREATE TABLE Customer (
customerID INTEGER CHECK (customerID > 0) PRIMARY KEY,
name VARCHAR(30) NOT NULL,
street VARCHAR(30) NOT NULL,
postcode SMALLINT CHECK (postcode > 0),
city VARCHAR(20)
);

Example Database ...
CREATE TABLE Producer (
name VARCHAR(40) PRIMARY KEY,
address VARCHAR(30)
);
CREATE TABLE Order (
orderID INTEGER CHECK (orderID > 0) PRIMARY KEY,
customerID INTEGER,
cdID INTEGER,
date DATE,
amount INTEGER,
Status VARCHAR(20) NOT NULL DEFAULT 'open',
UNIQUE (customerID, cdID, date),
FOREIGN KEY (customerID) REFERENCES Customer(customerID)
ON UPDATE CASCADE ON DELETE SET NULL,
FOREIGN KEY (cdID) REFERENCES CD(cdID)
ON UPDATE CASCADE
);

Example Database ...
CREATE TABLE CD (
cdID INTEGER PRIMARY KEY,
title VARCHAR(30) NOT NULL,
duration SMALLINT,
price SMALLINT,
year SMALLINT,
producer VARCHAR(40),
FOREIGN KEY (producer) REFERENCES Producer(name)
);

Embedded SQL
 The expressiveness of SQL can be enhanced by
embedding SQL statements into application code
 Use of a preprocessor
 transforms SQL statements into function calls in the host language
 type checks, syntax and semantic validation
 error handling
 Data interchange via shared variables
 shared variables are used in SQL statements as well as in
statements of the host language
 A special SQLSTATE variable is used to connect the host
language with the SQL execution engine

Embedded SQL Program Processing
 The preprocessor transforms a program with embedded
SQL statements into the host language
 e.g. nsqlprep.exe for ESQL-C
 The compiler produces the linked program object code
Host
language
with
Embedded
SQL
Host
language
with
function
calls
Program
object
code
Embedded SQL
preprocessor
Host language
compiler
SQL library

Call Level Interface
 SQL library functions are called directly
 not tied to particular DBMS (drivers stored separately)
 Various implementations exist
 SQL/CLI for C
 Open Database Connectivity (ODBC) and its successor OLE DB
 Java™ Database Connectivity (JDBC)
 ActiveX® Data Objects (ADO)

Java Database Connectivity (JDBC)
 The following JDBC packages are part of Java SE 8
 java.sql.*
- basic JDBC functionality for J2SE
 javax.sql.*
- supplemental extensions for J2EE
 The standardised Java API provides database
connectivity through vendor-specific drivers
 Limited code portability among SQL platforms due to
vendor-specific SQL dialects

Opening a JDBC Connection
 The JDBC URL varies for different drivers
 e.g. jdbc:microsoft:sqlserver for Microsoft SQL Server
public Connection openConnection() {
try {
Connection conn = DriverManager.getConnection(
"jdbc:microsoft:sqlserver://localhost:1433",
"fred",
"password");
return conn;
} catch (SQLException e) {
System.out.println("Opening JDBC Connection failed.");
return null;
}
}

Statements
 There are three different kinds of statements
 Statement
- general statement
 PreparedStatement
- precompiled statement
- more efficient if the same query is executed multiple times
 CallableStatement
- used to call stored procedures
 Methods for executing a statement
 executeUpdate(String sql)
 executeQuery(String sql)
 No parameters are required for PreparedStatements

Statements ...
void insertProducer(String name, String address) {
try {
Connection conn = this.openConnection();
Statement s = conn.createStatement();
s.executeUpdate("INSERT INTO Producer VALUES ('" + name + "', '"
+ address + "')");
System.out.println("Inserting "" + name + "" failed.");
}
}
public void insertProducer(String name, String address) {
try {
Statement s = conn.prepareStatement("INSERT INTO Producer VALUES ('"
+ name + "', " + address + ")");
s.executeUpdate();
System.out.println("Inserting "" + name + "" failed."); }
}

Result Set
 JDBC represents cursors as ResultSet
 API offers navigation methods on a ResultSet
 next(), previous()
 first(), last()
 absolute(int row), relative(int rows)
 API offers various get methods to fetch data as well as
update methods for common SQL data types

Result Set Example
 Note that it would be easier to use the SQL AVG operator
public float getAverageCDLength() {
float result = 0.0;
try {
Statement s = conn.createStatement();
ResultSet set = s.executeQuery("SELECT length FROM CD");
int i = 0;
while (set.next()) {
result += set.getInt(1);
i++;
}
return result/i;
System.out.println("Calculation of average length failed.");
return 0;
}
}

Parameter Parsing
 Prepared statements can be parameterised
 flexibility to use different values in a given query
 A question mark (?) is used as a placeholder in the query
string
 Various methods to insert data at runtime
 setString(int index, String s)
 setInt(int index, int i)
 setBoolean(int index, boolean b)
 setDate(int index, Date d)
 ...

Parameter Parsing Example
public void insertProducers(List<Producer> producers) {
try {
Statement s = conn.prepareStamement(
"INSERT INTO Producer(name, address) VALUES(?, ?)");
for (Producer producer : producers) {
s.setString(1, producer.getName());
s.setString(2, producer.getAddress());
s.executeUpdate();
}
System.out.println("Insertion of Producers failed.");
}
}

Special Datatypes and NULL Values
 Some SQL datatypes cannot be easily mapped to Java
datatypes
 JDBC offers implementations for these types
 Clob, Blob, Date, Time, Timestamp
 Null values are handled via special methods
 wasNull()
 updateNull(int index)
 setNull(int index, int sqlType)

JDBC Summary
 Concepts of ESQL and JDBC are similar
 State of the art for Java database programming
 Generic JDBC-ODBC driver if no specific JDBC driver is
available
 Java Data Objects (JDO)
 enables Java programmers to directly store their Java domain
model instances in a database
 hides SQL from the programmer
 http://java.sun.com/javase/technologies/database/

Application Logic on the Server Side
 Stored Procedures
 PL/SQL
- Oracle
 Transact-SQL
- Microsoft
 standardised as SQL/PSM in SQL-99
- Persistent Stored Modules
 Triggers
 event driven execution of application logic
 User Defined Types
 standardised in SQL-99

SQL Persistent Stored Modules
 SQL is extended with constructs known from high-level
programming languages
 assignments, branches, loops, subroutines and exceptions
createProcedure = "CREATE PROCEDURE" , name , "(" , parameters , ")" ,
localDeclarations , procedureBody;
createFunction = "CREATE FUNCTION" , name , "(" , parameters , ")" ,
"RETURNS" , type , localDeclarations , functionBody;

Parameters
 SQL/PSM defines three types for parameters
 IN
- input only
 OUT
- output only
 INOUT
- both input and output
 The default mode is IN
 Procedure parameters can have any mode
 Function parameters can have IN mode only
 result given back only via the return value

Procedure Example
 Procedure parameters can have any mode
 DB administrators often create these type of procedures
(for maintenance)
CREATE PROCEDURE RelocateProducer(
IN oldAddress VARCHAR(30),
IN newAddress VARCHAR(30)
)
UPDATE Producer
SET address = newAddress
WHERE address = oldAddress;

Function Example
CREATE FUNCTION AverageCDLengthOfProducer(
IN name VARCHAR(30),
)
RETURNS INTEGER
DECLARE result INTEGER;
BEGIN
SELECT AVG(length) INTO result
FROM CD
WHERE producer = name;
RETURN result;
END;

SQL/PSM Statements
 Procedure calls
 Function evaluation
 functions cannot be called
 functions are directly invoked as parts of expressions
 Return statement
 does not terminate the function
 additional RETURN statements may cause the return value to
change after an initial return statement
CALL name (arguments)
RETURN expression

SQL/PSM Statements ...
 Local variable declaration
 Assignments
 NULL is a permissible expression
 Compound statement
DECLARE name type
SET variable = expression
BEGIN ... END

Branch Statement
 If statement
 ELSEIFs and final ELSE are optional
IF condition THEN
statements
ELSEIF condition THEN
statements
ELSE
statements
ENDIF

Branch Example
CREATE FUNCTION IsExpensive(
IN cdTitle CHAR(30)
)
RETURNS BOOLEAN
IF NOT EXISTS(SELECT *
FROM CD
WHERE title = cdTitle) THEN
RETURN FALSE;
ELSEIF 50 < (SELECT MAX(price)
FROM CD
WHERE title = cdTitle) THEN
RETURN TRUE;
ELSE
RETURN FALSE;
ENDIF;

Loop Statements
 Basic loop statement
 The loop can be terminated with
LEAVE label
 the label identifies which loop has to be aborted
label: LOOP
statements
END LOOP

Loop Statements ...
 While loop statement
 Repeat loop statement
WHILE condition DO
statements
END WHILE
REPEAT
statements
UNTIL condition
END REPEAT

Loop Statements ...
 For loop statement
 Convenience statement to iterate over cursor
 open / close cursor
 check if more tuples to be fetched
 Name and cursor are needed for transformation into
basic loop (by PSM interpreter)
FOR name AS cursor CURSOR FOR
query
DO
statements
END FOR

Loop Example
CREATE FUNCTION LengthVarianceOfProducer(
IN name VARCHAR(40),
) RETURNS REAL
DECLARE variance REAL;
DECLARE mean REAL;
DECLARE count INTEGER;
BEGIN
SET variance = 0.0; SET mean = 0.0;
SET count = 0;
FOR cdLoop AS cdCursor CURSOR FOR
SELECT length FROM CD WHERE producer = name;
DO
SET count = count + 1;
SET variance = variance + length * length;
SET mean = mean + length;
END FOR;
SET mean = mean/count;
RETURN variance/count – mean * mean;
END;

SQL/PSM Summary
 Perform computation on the server side
 Implement functionality not contained in SQL
 recursion
 closure
 mathematical and statistical functions
 SQL in combination with SQL/PSM forms a
Turing complete programming language
 Functionality for administrative tasks is often
implemented as PSM

Transitive Closure (Recursion)
 Inconvenient to specify transitive closure using iteration
 Since SQL:1999 there is a form of recursion using the
WITH RECURSIVE clause
 Example
 "Find all destinations that can be reached (directly or indirectly)
from Zurich Airport"
from to
ZRH BRU
ZRH JFK
BRU CDG
JFK BRU
... ...
Flight

Transitive Closure (Recursion) ...
 Recursive view is a union of two subqueries
 base query
 recursive query making use of the recursive view
- recursive query should be monotonic (e.g. no aggregation in recursive view)
 Repeat until no new tuples added and fixpoint is reached
WITH RECURSIVE Connection(from, to) AS (
SELECT from, to
FROM Flight
UNION
SELECT Flight.from, Connection.to
FROM Flight, Connection
WHERE Flight.to = Connection.from
)
SELECT DISTINCT to
FROM Connection
WHERE Connection.from = 'ZRH';

Triggers
 A trigger is a statement that the DBMS executes as a
side effect of a modification to the database
 The definition of a trigger follows the so-called
event-condition-action (ECA) model
 event
- specifies the signal that triggers the rule (e.g. insert, update or delete)
 condition
- the condition that has to be satisfied for the execution of the action
 action
- the action to be executed
 Triggers are a powerful tool for checks before/after an
operation on a relation (e.g. for integrity constraints)

Triggers ...
 Example
 When data is restored from a backup or replicated,
triggers often have to be disabled
 otherwise triggers might be executed multiple times
 The execution of a trigger can lead to a (infinitite)
cascade of other triggers that get fired
 often the length of such a trigger chain is limited by the system
CREATE TRIGGER setNull BEFORE UPDATE ON Producer
REFERENCING NEW ROW AS newRow
FOR EACH ROW
WHEN newRow.address = '' SET newRow.address = NULL;

Homework
 Study the following chapter of the
Database System Concepts book
 chapter 5
- sections 5.1-5.4, 5.7
- Advanced SQL

Exercise 6
 Structured Query Language (SQL)


References
 A. Silberschatz, H. Korth and S. Sudarshan,
Database System Concepts (Sixth Edition),
McGraw-Hill, 2010
 H. Garcia-Molina, J.D. Ullman and J. Widom, Database
Systems: The Complete Book, Prentice Hall, 2002

2 December 2005
Next Lecture
DBMS Architectures and Features

Advanced SQL - Lecture 6 - Introduction to Databases (1007156ANR)

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