Application Users. Application Programs. Some Reasons for Using a DBMS (Database Management System)

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1 Brief Introduction to DATABASE 1. What is a Database System? Application Users Application Programs Database Management System Database Management System database Some Reasons for Using a DBMS (Database Management System) Persistence of data Sharing of data between programs Handle concurrent requests for data access Transactions that can be committed or rolled back Report generation Sometimes database means a program for managing data Example: Oracle Corporation is a database company. MySQL is a database. Sometimes database means a collection of data Example: I keep a database of my CD collection on 3 by 5 cards Sometimes database means a set of tables, indexes, and views Example: My program needs to connect to the Airline Reservation database, which uses MySQL 2. Types of Databases Relational: Data is stored in tables 1

2 Object-Oriented: Tables can be classed and/or sub-classed, and Programmer can define methods on tables Object: Objects are stored in the database 3. Relational, Object-Relational, O-O Databases and SQL Database consists of a number of tables. Table is a collection of records. Each column of data has a type Firstname Lastname Phone Code Bill Clinton George Bush John Kelly Use SQL (Structured Query Language) to access data in the database Some Available DBMS systems Oracle, MySQL, DB2, SQL Server, Access, Sybase, etc. Some Open Source DBMS Systems Postgres, MySQL community server (??) 4. Rational Database and Relational Data Model Most of today s database systems are relational database systems, based on the relational data model. A relational data model has three key components: structure, integrity and languages. Structure defines the representation of the data. Integrity imposes constraints on the data. Language provides the means for accessing and manipulating data. Relational Structure A relational database consists of a set of relations. A relation has two things in one: a schema and an instance of the schema. The schema defines the relation and an instance is the content of the relation at a given time. An instance of a relation is nothing more than a table with rows and named columns. For convenience with no confusion, we refer instances of relations as just relations or tables. 2

3 Course Table Relation/Table Name Columns/Attributes Course Table Tuples/ Rows courseid subjectid coursenumber title numofcredits CSCI 1301 Introduction to Java I CSCI 1302 Introduction to Java II CSCI 3720 Database Systems CSCI 4750 Rapid Java Application MATH 2750 Calculus I MATH 3750 Calculus II EDUC 1111 Reading ITEC 1344 Database Administration 3 Student Table Student Table ssn firstname mi lastname phone birthdate street zipcode deptid Jacob R Smith Kingston Street BIOL John K Stevenson null 100 Main Street BIOL George K Smith Abercorn St CS Frank E Jones Main Street BIOL Jean K Smith Main Street CHEM Josh R Woo Franklin St CHEM Josh R Smith Main Street BIOL Joy P Kennedy Bay Street CS Toni R Peterson Bay Street MATH Patrick R Stoneman Washington St MATH Rick R Carter West Ford St BIOL 3

4 Enrollment Table Enrollment Table ssn courseid dateregistered grade A B C D F A B C D A A B F F D D A D B Table vs. File NOTE: A table or a relation is not same as a file. Most of the relational database systems store multiple tables in a file. Integrity Constraints An integrity constraint imposes a condition that all legal instances of the relations must satisfy. In general, there are three types of constraints: domain constraint, primary key constraint, and foreign key constraint. Domain constraints and primary key constraints are known as intra-relational constraints, meaning that a constraint involves only one relation. The foreign key constraint is known as inter-relational, meaning that a constraint involves more than one relation. 4

5 Domain Constraints, Primary Key Constraints, Foreign Key Constraints Enrollment Table ssn courseid dateregistered grade A B C... Course Table Each value in courseid in the Enrollment table must match a value in courseid in the Course table courseid subjectid coursenumber title numofcredits CSCI 1301 Introduction to Java I CSCI 1302 Introduction to Java II CSCI 3720 Database Systems 3... Each row must have a value for couserid, and the value must be unique Each value in the numofcredits column must be greater than 0 and less than 5 Domain Constraints Domain constraints specify the permissible values for an attribute. Domains can be specified using standard data types such as integers, floating-point numbers, fixed-length strings, and variant-length strings. The standard data type specifies a broad range of values. Additional constraints can be specified to narrow the ranges. You can also specify whether an attribute can be null. Example create table Course( subjectcode char(4) not null, coursenumber int not null, title varchar(50) not null, numofcredits int not null constraint greaterthanone check (numofcredits >= 1)); Superkey A superkey is an attribute or a set of attributes that uniquely identify the relation. That is, no two tuples have the same values on the superkey. By definition, a relation consists of a set of distinct tuples. The set of all attributes in the relation forms a superkey. Key and Candidate Key 5

6 A key K is a minimal superkey, meaning that any proper subset of K is not a superkey. It is possible that a relation has several keys. In this case, each of the keys is called a candidate key. Primary Key The primary key is one of the candidate keys designated by the database designer. The primary key is often used to identify tuples in a relation. create table Course( subjectcode char(4), coursenumber int, title varchar(50), numofcredits int constraint greaterthanone check (numofcredits >= 1), primary key (subjectcode, coursenumber)); Primary Key Constraints The primary key constraint specifies that the primary key value of a tuple cannot be null and no two tuples in the relation can have the same value on the primary key. The DBMS enforces the primary key constraint. For example, if you attempt to insert a record with the same primary key as an existing record in the table, the DBMS would report an error and reject the operation. Foreign Key Constraints In a relational database, data are related. Tuples in a relation are related and tuples in different relations are related through their common attributes. Informally speaking, the common attributes are foreign keys. The foreign key constraints define the relationships among relations. Formally, a set of attributes FK is a foreign key in a relation R that references relation T if it satisfies the following two rules: 1. The attributes in FK have the same domain as the primary key in T. 2. A non-null value on FK in R must match a primary key value in T. R FK T create table Enrollment ( ssn char(9), courseid char(5), dateregistered date, 6

7 grade char(1), primary key (ssn, courseid), foreign key (ssn) references Student, foreign key (courseid) references Course ); A foreign key is not necessarily the primary key or part of the primary in the relation. For example, subjectcode is a foreign key in the Course table that references the Subject table, but it is not the primary key in Course. departmentcode is a foreign key in the Subject table that references Department, but it is not the primary key in Subject. The referencing relation and the referenced relation may be the same table. For example, supervisorid is a foreign key in Faculty that references facultyid in Faculty. The foreign key is not necessary to have the same name as its referenced primary key as long as they have the same domain. For example, headid is a foreign key in Department that references facultyid in Faculty. A relation may have more than one foreign key. For example, headid and collegecode are both foreign keys in Department. 5. SQL History Evolution of the SQL Standard o First standard approved in 1989 (called SQL-89 or SQL1) o Comprehensive revision in 1992 (SQL-92 or SQL2) o Third big revision in 1999 (SQL-99 known as SQL3) o Other revisions known as SQL:2003, SQL:2006 (XML features), SQL:2008 (more object DB features) Origins of SQL o Originally called SEQUEL (Structured English Query Language), then SQL (Structured Query Language) o Developed at IBM Research for experimental relational DBMS called System-R in the 1970s 6. SQL Data Definition and Data Types CREATE statement can be used to: o Create a named database schema o Create individual database tables and specify data types for the table attributes, as well as key, referential integrity, and NOT NULL constraints o Create named constraints Other commands can modify the tables and constraints o DROP and ALTER statements (e.g., Example: ALTER TABLE EMPLOYEE ADD COLUMN JOB VARCHAR(12); The database users must enter values for the new attribute JOB for each EMPLOYEE tuple. 7

8 7. Schema and Catalog Concepts in SQL An SQL schema is identified by a schema name, and includes an authorization identifier to indicate the user or account who owns the schema, as well as descriptors for each element in the schema. Schema elements include tables, constraints, views, domains, and other constructs (such as authorization grants) that describe the schema. Example: CREATE SCHEMA COMPANY AUTHORIZATION JSmith ; Catalog a named collection of schemas in an SQL environment. SQL environment is an installation of an SQL-compliant RDBMS in a computer system. A catalog always contains a special schema called INFORMATION-SCHEMA The CREATE SCHEMA Statement A DBMS can manage multiple databases DBA (or authorized users) can use CREATE SCHEMA to have distinct databases; for example: CREATE SCHEMA COMPANY AUTHORIZATION 'JSmith'; Each database has a schema name (e.g. COMPANY) User 'Smith' will be owner of schema, can create tables, other constructs in that schema Table names can be prefixed by schema name if multiple schemas exist (e.g. COMPANY.EMPLOYEE) Prefix not needed if there is a default schema for the user The CREATE TABLE Command in SQL In its simplest form, specifies a new base relation by giving it a name, and specifying each of its attributes and their data types (INTEGER, FLOAT, DECIMAL(i,j), CHAR(n), VARCHAR(n), DATE, and other data types) A constraint NOT NULL may be specified on an attribute CREATE TABLE DEPARTMENT ( DNAME VARCHAR(15) NOT NULL, DNUMBER INT NOT NULL, MGRSSN CHAR(9) NOT NULL, MGRSTARTDATE DATE ); CREATE TABLE can also specify the primary key, UNIQUE keys, and referential integrity constraints (foreign keys) Via the PRIMARY KEY, UNIQUE, and FOREIGN KEY phrases CREATE TABLE DEPARTMENT ( DNAME VARCHAR(15) NOT NULL, DNUMBER INT NOT NULL, MGRSSN CHAR(9) NOT NULL, MGRSTARTDATE DATE, PRIMARY KEY (DNUMBER), UNIQUE (DNAME), FOREIGN KEY(MGRSSN) REFERENCES EMPLOYEE (SSN)); 8

9 Indices Indices make accessing faster Primary keys automatically have an index The CREATE INDEX command creates indices CREATE INDEX dname_index on DEPARTMENT (DNAME); 8.Understanding Database based on MySQL Connecting to the Database Can be done with: Mysql command line tool - mysql GUI clients Program Examples (by MySQL command line tool) You can choose mysqld as a service, or mysqld as a standalone daemon. mysqld --standalone C:\mysql\bin\mysqld --standalone debug mysqladmin" p -u root shutdown $mysql h localhost u user p GUI Clients MySQL Workbench SQL Syntax Names Databases, table columns & indexes have names Legal Characters Alphanumeric characters, '_', '$' Names can start with: Letter Underscore Letter with diacritical marks and some non-latin letters Name length 64 characters - MySQL Names are not case sensitive 9

10 Data Types Numeric Values Integer: decimal or hexadecimal Floating-point: scientific, real number (e.g., ) String Values MySQL example: this is a string or this is a string Escape Sequence \' Single quote \b Backspace \n Newline \r Tab \\ Backslash Comments (MySQL example) -- this is a comment /* this is a comment */ #this is a comment Numeric Data Types Numeric(10, 2) defines a number with maximum of 10 digits with 2 of the 10 to the right of the decimal point (e.g., ) Decimal and numeric are different names for the same type. 10

11 String Types Type char(n) varchar(n) text Blob (MySQL) Description Fixed-length blank padded Variable-length with limit Variable unlimited length Variable (not specifically limited) length binary string char & varchar are the most common string types char is fixed-width: shorter strings are padded (with blanks) text can be of any size MySQL limits char and varchar to 255 characters Dates DATETIME YYYY-MM-DD HH:MM DATE YYYY-MM-DD format TIMESTAMP Basically now is same as DATETIME Common SQL Statements SELECT INSERT UPDATE DELETE CREATE TABLE DROP TABLE ALTER TABLE CREATE INDEX DROP INDEX CREATE VIEW DROP VIEW Retrieves data from table(s) Adds row(s) to a table Change field(s) in record(s) Removes row(s) from a table Data Definition Define a table and its columns (fields) Deletes a table Adds a new column, add/drop primary key Create an index Delete an index Define a logical table from other table(s) view(s) Deletes a view CREATE DATABASE General Form CREATE DATABASE [IF NOT EXISTS] db_name [create_specification [, create_specification]...] create_specification: [DEFAULT] CHARACTER SET charset_name [DEFAULT] COLLATE collation_name (Example) mysql> create database DBMSExamples; Query OK, 1 row affected (0.00 sec) 11

12 USE Sets a default database for subsequent queries General Form USE db_name (Example) mysql> use DBMSExamples; Database changed CREATE TABLE General Form CREATE TABLE table_name ( col_name col_type [ NOT NULL PRIMARY KEY] [, col_name col_type [ NOT NULL PRIMARY KEY]]* ) mysql> use DBMSExamples; Database changed (Example) Mysql> CREATE TABLE students -> ( -> firstname CHAR(20) NOT NULL, -> lastname CHAR(20), -> phone CHAR(10), -> code INTEGER -> ); Query OK, 0 rows affected (0.61 sec) mysql> CREATE TABLE codes -> ( -> code INTEGER, -> name CHAR(20) -> ); Query OK, 0 rows affected (0.63 sec) mysql> DESCRIBE students -> ; Field Type Null Key Default Extra firstname char(20) NO lastname char(20) YES NULL phone char(10) YES NULL code int(11) YES NULL

13 4 rows in set (0.11 sec) mysql> desc students; Field Type Null Key Default Extra firstname char(20) NO lastname char(20) YES NULL phone char(10) YES NULL code int(11) YES NULL rows in set (0.00 sec) mysql> explain students -> \g Field Type Null Key Default Extra firstname char(20) NO lastname char(20) YES NULL phone char(10) YES NULL code int(11) YES NULL rows in set (0.00 sec) mysql> show columns from students -> ; Field Type Null Key Default Extra firstname char(20) NO lastname char(20) YES NULL phone char(10) YES NULL code int(11) YES NULL rows in set (0.02 sec) mysql> show fields from students \g Field Type Null Key Default Extra firstname char(20) NO lastname char(20) YES NULL phone char(10) YES NULL code int(11) YES NULL rows in set (0.00 sec) SELECT Gets the data from one or more tables 13

14 General Form SELECT [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT] [SQL_CACHE SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS] [HIGH_PRIORITY] [DISTINCT DISTINCTROW ALL] select_expression,... [INTO {OUTFILE DUMPFILE} 'file_name' export_options] [FROM table_references [WHERE where_definition] [GROUP BY {unsigned_integer col_name formula} [ASC DESC],... [WITH ROLLUP]] [HAVING where_definition] [ORDER BY {unsigned_integer col_name formula} [ASC DESC],...] [LIMIT [offset,] row_count row_count OFFSET offset] [PROCEDURE procedure_name(argument_list)] [FOR UPDATE LOCK IN SHARE MODE]] mysql> SELECT * FROM students; Empty set (0.00 sec) INSERT Add data to a table General Form INSERT [LOW_PRIORITY DELAYED] [IGNORE] [INTO] tbl_name [(col_name,...)] VALUES ((expression DEFAULT),...),(...),... [ ON DUPLICATE KEY UPDATE col_name=expression,... ] (Example) mysql> INSERT -> INTO students (firstname, lastname, phone. Code) -> VALUES ('bill', 'clinton', ' ,2000); Query OK, 1 row affected (0.50 sec) mysql> INSERT -> INTO codes (code, name) -> VALUES (2000, 'marginal' ); Query OK, 1 row affected (0.48 sec) mysql> SELECT firstname, phone FROM students; firstname phone bill row in set (0.00 sec) 14

15 mysql> SELECT lastname, name -> FROM students, codes -> WHERE students.code = codes.code; lastname name clinton marginal row in set (0.01 sec) mysql> SELECT students.lastname, codes.name -> FROM students, codes -> WHERE students.code = codes.code; lastname name clinton marginal row in set (0.44 sec) mysql> Update Modify existing data in a database General Form UPDATE [LOW_PRIORITY] [IGNORE] tbl_name [, tbl_name...] SET col_name1=expr1 [, col_name2=expr2...] [WHERE where_definition] Example mysql> update students -> set firstname='hilary' -> where lastname="clinton"; Query OK, 1 row affected (0.52 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from students; firstname lastname phone code Hilary clinton row in set (0.00 sec) mysql> ALTER TABLE students ADD column foo CHAR(40); Query OK, 1 row affected (0.03 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> DROP TABLE students; 15

16 Query OK, 0 rows affected (0.01 sec) mysql> DROP DATABASE databaseexamples; Query OK, 0 rows affected (0.00 sec) 9. JDBC (Java Database Connectivity-- Connecting to DBMS) Oracle JDBC Tutorial & Documentation Connector-J, MySql JDBC Driver Documentation, JDBC Drivers Java supports four types of JDBC drivers JDBC-ODBC bridge plus ODBC driver: Java code access ODBC native binary drivers, ODBC driver accesses databases, ODBC drivers must be installed on each client Native-API partly-java driver: Java code accesses database specific native binary drivers JDBC-Net pure Java driver: Java code accesses database via DBMS-independent net protocol Pure Java driver In a pure Java-based driver that communicates directly with vendor's database through socket connection. This is the highest performance driver available for the database and is usually provided by the vendor itself. 16

17 This kind of driver is extremely flexible, you don't need to install special software on the client or server. Further, these drivers can be downloaded dynamically. MySQL's Connector/J driver is a Type 4 driver. Because of the proprietary nature of their network protocols, database vendors usually supply type 4 drivers. The JDBC API is comprised of two packages: java.sql javax.sql The JDBC Interfaces Driver Connection Connection Statement Statement Statement Statement ResultSet ResultSet ResultSet ResultSet 17

18 Developing JDBC Programs Statement to load a driver: Class.forName("JDBCDriverClass"); A driver is a class. For example: Database Driver Class Source Access sun.jdbc.odbc.jdbcodbcdriver Already in JDK MySQL com.mysql.jdbc.driver Oracle oracle.jdbc.driver.oracledriver Connection connection = DriverManager.getConnection(databaseURL); Database Access MySQL Oracle URL Pattern jdbc:odbc:datasource jdbc:mysql://hostname/dbname jdbc:oracle:thin:@hostname:port#:oracledbsid Examples: For Access: Connection connection = DriverManager.getConnection ("jdbc:odbc:examplemdbdatasource"); For MySQL: Connection connection = DriverManager.getConnection ("jdbc:mysql://localhost/test"); For Oracle: Connection connection = DriverManager.getConnection ("jdbc:oracle:thin:@company.com:1521:orcl", "bob", "feiner"); Creating statement: Statement statement = connection.createstatement(); Executing statement (for update, delete, insert): statement.executeupdate ("create table Temp (col1 char(5), col2 char(5))"); Executing statement (for select): // Select the columns from the Student table ResultSet resultset = statement.executequery ("select firstname, mi, lastname from Student where lastname " + " = 'Smith'"); Executing statement (for select): // Select the columns from the Student table ResultSet resultset = stmt.executequery 18

19 ("select firstname, mi, lastname from Student where lastname " + " = 'Smith'"); Processing ResultSet (for select): // Iterate through the result and print the student names while (resultset.next()) System.out.println(resultSet.getString(1) + " " + resultset.getstring(2) + ". " + resultset.getstring(3)); Queries executeupdate Use for INSERT, UPDATE, DELETE or SQL that return nothing executequery Use for SQL (SELECT) that return a result set execute Use for SQL that return multiple result sets Uncommon ResultSet ResultSet - Result of a Query - JDBC returns a ResultSet as a result of a query - A ResultSet contains all the rows and columns that satisfy the SQL statement - A cursor is maintained to the current row of the data 19

20 - The cursor is valid until the ResultSet object or its Statement object is closed - next() method advances the cursor to the next row - You can access columns of the current row by index or name ResultSet has getxxx methods that: has either a column name or column index as argument returns the data in that column converted to type XXX getobject - An alternative to the getxxx method Rather than ResultSet tablelist = gettables.executequery("select * FROM name"); String firstname = tablelist.getstring( 1); - Can use ResultSet tablelist = gettables.executequery("select * FROM name"); String firstname = (String) tablelist.getobject( 1); getobject( int k) returns the object in the k th column of the current row getobject( String columnname) returns the object in the named column PreparedStatement The PreparedStatement interface is designed to execute dynamic SQL statements and SQL-stored procedures with IN parameters. These SQL statements and stored procedures are precompiled for efficient use when repeatedly executed. Statement pstmt = connection.preparestatement ("insert into Student (firstname, mi, lastname) + values (?,?,?)"); Retrieving Database Metadata Database metadata is the information that describes database itself. JDBC provides the DatabaseMetaData interface for obtaining database wide information and the ResultSetMetaData interface for obtaining the information on the specific ResultSet. The DatabaseMetaData interface provides more than 100 methods for getting database metadata concerning the database as a whole. These methods can be divided into three groups: for retrieving general information, for finding database capabilities, and for getting object descriptions. The general information includes the URL, username, product name, product version, driver name, driver version, available functions, available data types and so on. Example: DatabaseMetaData dbmetadata = connection.getmetadata(); 20

21 System.out.println("database URL: " + dbmetadata.geturl()); System.out.println("database username: " + dbmetadata.getusername()); System.out.println("database product name: " + dbmetadata.getdatabaseproductname()); System.out.println("database product version: " + dbmetadata.getdatabaseproductversion()); System.out.println("JDBC driver name: " + dbmetadata.getdrivername()); System.out.println("JDBC driver version: " + dbmetadata.getdriverversion()); System.out.println("JDBC driver major version: " + new Integer(dbMetaData.getDriverMajorVersion())); System.out.println("JDBC driver minor version: " + new Integer(dbMetaData.getDriverMinorVersion())); System.out.println("Max number of connections: " + new Integer(dbMetaData.getMaxConnections())); System.out.println("MaxTableNameLentgh: " + new Integer(dbMetaData.getMaxTableNameLength())); System.out.println("MaxColumnsInTable: " + new Integer(dbMetaData.getMaxColumnsInTable())); connection.close(); CallableStatement The CallableStatement interface is used to execute SQL-stored procedure/function. Example: drop function if exists studentfound; delimiter // create function studentfound(first VARCHAR(20), last VARCHAR(20)) returns int begin declare result int; select count(*) into result from Student where Student.firstName = first and Student.lastName = last; return result; end; // 21

22 delimiter ; mysql> select studentfound('king', 'Smith'); CallableStatement callablestatement = conn.preparecall( "{? = call studentfound(?,?)}"); java.util.scanner input = new java.util.scanner(system.in); String firstname = "Jacob"; String lastname = "Smith"; callablestatement.setstring(2, firstname); callablestatement.setstring(3, lastname); callablestatement.registeroutparameter(1, Types.INTEGER); callablestatement.execute(); if (callablestatement.getint(1) >= 1) { out.println(firstname + " " + lastname + " is in the database" + "<br>"); } else { out.println(firstname + " " + lastname + " is not in the database" + "<br>"); Data Conversion 22

23 Some Cautions Mixing ResultSets Can't have two active result sets on same statement Connection rugby; rugby = DriverManager.getConnection( dburl, user, password); Statement gettables = rugby.createstatement(); ResultSet count = gettables.executequery("select COUNT(*) FROM name"); ResultSet tablelist = gettables.executequery("select * FROM name"); while (tablelist.next() ) System.out.println("Last Name: " + tablelist.getobject(1) + '\t' + "First Name: " + tablelist.getobject( "first_name")); // Raises java.sql.sqlexception count.getobject(1); rugby.close(); this can happen when two threads have access to the same statement Two Statements on one Connection work Connection rugby; rugby = DriverManager.getConnection( dburl, user, password); Statement gettables = rugby.createstatement(); Statement tablesize = rugby.createstatement(); ResultSet count = gettables.executequery("select COUNT(*) FROM name"); ResultSet tablelist = tablesize.executequery("select * FROM name"); while (tablelist.next() ) System.out.println("Last Name: " + tablelist.getobject(1) + '\t' + "First Name: " + tablelist.getobject( "first_name")); count.next(); System.out.println("Count: " + count.getobject(1) ); count.close(); tablelist.close(); rugby.close(); Threads & Connections - Some JDBC drivers are not thread safe - If two threads access the same connection results may get mixed up MySql driver is thread safe - When two threads make a request on the same connection - The second thread blocks until the first thread get it its results - Can use more than one connection but - Each connection requires a process on the database 23

24 10. Some Data Modeling Terms and JOIN operations Entity: a distinct class of things about which something is known Entity Occurrence: particular instance of an entity class. In a database entity occurrences are records in a table Attribute: an abstraction belonging to or characteristic of an entity Primary Key (unique identifier): an attribute (or set of attributes) that uniquely defines an entity Relationship: an abstraction belonging to or characteristic of two entities or parts together Foreign Key: a unique identifier in a record representing another record Entity Relationship (ER) Diagram Crow s Foot ERD Entity (car) with: Attributes (Color, make, model, serial number) Primary key (serial number) Relationship between Car and Person entities. Car must have one and only one owner. Person may own zero, one or more cars. Person can own many cars 24

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26 ER to Relational mapping ER-to-Relational Mapping Algorithm COMPANY database example Assume that the mapping will create tables with simple single-valued attributes Step 1: Mapping of Regular Entity Types For each regular entity type, create a relation R that includes all the simple attributes of E Called entity relations Each tuple represents an entity instance Step 2: Mapping of Weak Entity Types For each weak entity type, create a relation R and include all simple attributes of the entity type as attributes of R Include primary key attribute of owner as foreign key attributes of R Step 3: Mapping of Binary 1:1 Relationship Types For each binary 1:1 relationship type Identify relations that correspond to entity types participating in R Possible approaches: Foreign key approach Merged relationship approach Crossreference or relationship relation approach 26

27 Step 4: Mapping of Binary 1:N Relationship Types For each regular binary 1:N relationship type Identify relation that represents participating entity type at N-side of relationship type Include primary key of other entity type as foreign key in S Include simple attributes of 1:N relationship type as attributes of S Alternative approach Use the relationship relation (cross-reference) option as in the third option for binary 1:1 relationships Step 5: Mapping of Binary M:N Relationship Types For each binary M:N relationship type Create a new relation S Include primary key of participating entity types as foreign key attributes in S Include any simple attributes of M:N relationship type Step 6: Mapping of Multivalued Attributes For each multivalued attribute Create a new relation Primary key of R is the combination of A and K If the multivalued attribute is composite, include its simple components Step 7: Mapping of N-ary Relationship Types For each n-ary relationship type R Create a new relation S to represent R Include primary keys of participating entity types as foreign keys Include any simple attributes as attributes 27

28 JOIN Operations Primary Key A primary key is one that uniquely identifies a row in a table. A Simple Faculty Table name Brown 1 Clinton 2 Bush 3 faculty_id CREATE TABLE faculty ( name CHAR(20) NOT NULL, faculty_id INTEGER AUTO_INCREMENT PRIMARY KEY ); Adding Values INSERT INTO faculty ( name) VALUES ('White'); INSERT INTO faculty ( name) VALUES ('Beck'); INSERT INTO faculty ( name) VALUES ('Anantha'); INSERT INTO faculty ( name) VALUES ('Vinge'); select * from faculty; 28

29 Result name faculty_id White 1 Beck 2 Anantha 3 Vinge 4 (4 rows) CREATE TABLE office_hours ( start_time TIME NOT NULL, end_time TIME NOT NULL, day CHAR(3) NOT NULL, faculty_id INTEGER REFERENCES faculty, office_hour_id INTEGER AUTO_INCREMENT PRIMARY KEY ); faculty_id is a foreign key REFERENCES faculty insures that only valid references are made start_time end_time day faculty_id office_hour_id 10:00 11:00 Wed 1 1 8:00 12:00 Mon :00 18:30 Tue 1 3 9:00 10:30 Tue 3 4 9:00 10:30 Thu :00 16:00 Fri 1 6 INSERT INTO office_hours ( start_time, end_time, day, faculty_id ) VALUES ( '10:00:00', '11:00:00', 'Wed', 1 ); The problem is that we need to know the id for the faculty Using Select INSERT INTO office_hours (start_time, end_time, day, faculty_id ) SELECT '8:00:00' AS start_time, '12:00:00' AS end_time, 'Fri' AS day, faculty_id AS faculty_id FROM 29

30 faculty WHERE name = 'Beck'; Getting Office Hours SELECT name, start_time, end_time, day FROM office_hours, faculty WHERE faculty.faculty_id = office_hours.faculty_id; mysql> SELECT -> name, start_time, end_time, day -> FROM -> office_hours, faculty -> WHERE -> faculty.faculty_id = office_hours.faculty_id; name start_time end_time day White 10:00:00 11:00:00 Wed Beck 08:00:00 12:00:00 Mon White 17:00:00 12:30:00 Tue Anantha 09:00:00 10:30:00 Tue Anantha 09:00:00 10:30:00 Thu White 15:00:00 16:00:00 Fri rows in set (0.00 sec) mysql> name start_time end_time day Whitney 10:00:00 11:00:00 Wed Beck 08:00:00 12:00:00 Mon Whitney 17:00:00 18:30:00 Tue Whitney 15:00:00 16:00:00 Fri Anantha 09:00:00 10:30:00 Tue Anantha 09:00:00 10:30:00 Thu Some Selection SELECT name, start_time, end_time, day FROM office_hours, faculty WHERE 30

31 faculty.faculty_id = office_hours.faculty_id AND start_time > '09:00:00' AND end_time < '16:30:00' ORDER BY Name; name start_time end_time day white 10:00:00 11:00:00 Wed white 15:00:00 16:00:00 Fri Joins People id first_name last_name 1 Roger Whitte 2 Leland Beck 3 Carl Eckberg _Addresses id user_name host person_id 1 beck cs.lehman.edu 2 2 white cs.lehman.edu 1 3 white cs2.lehman.edu 1 4 foo cs2.lehman.edu The tables have a column in common as _addresses.person_id refers to people.id. So we can create a new table by joining the two tables together on that column Inner Join (or just Join) Only uses entries linked in two tables first_name last_name user_name host Leland Beck beck cs.sdsu.edu Roger white white cs.sdsu.edu Roger White white rohan.sdsu.edu select first_name, last_name, user_name, host from people, _address where 31

32 Outer Join people.id = _address.person_id; or equivalently select first_name, last_name, user_name, host from people inner join _address on (people.id = _address.person_id); mysql> select -> first_name, last_name, user_name, host -> from -> people, _address -> where -> people.id = _address.person_id; first_name last_name user_name host Leland Beck beck cs.lehman.edu Roger White white cs.lehman.edu Roger White white cs2.lehman.edu rows in set (0.00 sec) mysql> select -> first_name, last_name, user_name, host -> from -> people inner join _address -> on -> (people.id = _address.person_id); first_name last_name user_name host Leland Beck beck cs.lehman.edu Roger White white cs.lehman.edu Roger White white cs2.lehman.edu rows in set (0.00 sec) mysql> Uses all entries from a table Left Outer Join Use all entries from the left table 32

33 first_name last_name user_name host Leland Beck beck cs.lehman.edu Roger White white cs.lehman.edu Roger White white cs2.lehman.edu Carl Eckberg select first_name, last_name, user_name, host from people left outer join _address on (people.id = _address.person_id); Right Outer Join first_name last_name user_name host Leland Beck beck cs.lehman.edu Roger white white cs.lehman.edu Roger Whitney whitney cs2.lehman.edu foo cs2..lehman.edu Use all entries from the right table select first_name, last_name, user_name, host from people right outer join _address on (people.id = _address.person_id); A right outer join B & B left outer join A The following two statements are equivalent select first_name, last_name, user_name, host from people right outer join _address on (people.id = _address.person_id); select first_name, last_name, user_name, host 33

34 from _address left outer join people on (people.id = _address.person_id); 11. Normalization The normal forms defined in relational database theory represent guidelines for record design. The guidelines corresponding to first through fifth normal forms are presented here, in terms that do not require an understanding of relational theory. The design guidelines are meaningful even if one is not using a relational database system. We present the guidelines without referring to the concepts of the relational model in order to emphasize their generality, and also to make them easier to understand. Our presentation conveys an intuitive sense of the intended constraints on record design, although in its informality it may be imprecise in some technical details. The normalization rules are designed to prevent update anomalies and data inconsistencies. With respect to performance tradeoffs, these guidelines are biased toward the assumption that all nonkey fields will be updated frequently. They tend to penalize retrieval, since data which may have been retrievable from one record in an un-normalized design may have to be retrieved from several records in the normalized form. There is no obligation to fully normalize all records when actual performance requirements are taken into account. 1 st, 2 nd, 3 rd, BCNF will be discussed. 12. Object relational Mapping (ORM) Will be updated 13. Views, Stored Procedures(Functions), Trigger Examples will be added if necessary 34