Database

Basic Definitions Database: A collection of related data. Database Management System (DBMS): A software package/ system to facilitate the creation and maintenance of a computerized database. Database System: The DBMS software together with the data itself. Sometimes, the applications are also included. ( Software + Database ) 2

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Relational Database 4

Data Models High Level or Conceptual data models provide concepts that are close to the way many users perceive data, entities, attributes and relationships. (Ex. ERD) Physical data models describes how data is stored in the computer and the access path needed to access and search for data. 5

Entity Relationship Diagram [ERD]

Entity Relationship Modeling Entity-Relationship Diagram (ERD): Identifies information required by the business by displaying the relevant entities and the relationships between them. 7

Entity Relationship Modeling, (Cont.) In building a data model a number of questions must be addressed: –What entities need to be described in the model? –What characteristics or attributes of those entities need to be recorded? –Can an attribute or a set of attributes be identified that will uniquely identify one specific occurrence of an entity? –What associations or relationships exist between entities? 8

Entity An entity is a thing that exists and is distinguishable -- an object, something in the environment. Examples : book, item, student Types of entities: –Regular entity (Strong entity): if its existence does not depend on another entity. –Weak entity: if its existence depends on another entity. 9

Attribute An entity has a set of attributes Attribute defines property of an entity It is given a name Attribute has value for each entity and value may change over time Example : BOOK entity has the following attributes ( TITLE, ISBN, AUTHOR, PUBLISHER, YEAR, PRICE) 10

Attribute Types Simple: Each entity has a single atomic value for the attribute ; e.g., SSN Composite: The attribute may be composed of several components ; e.g., Name (FirstName, MiddleName, LastName) Multi-valued: The attribute may has more than one value for a given entity; e.g., a book may have many authors Derived attributes: The attributes whose values are generated from other attributes using calculations ; e.g., Age is derived by subtracting current date from birthdate 11

Primary Key: an attribute of an entity type for which each entity must have a unique value; e.g., SSN of EMPLOYEE. Composite key: e.g., ID is a key of the applicant entity type with components (National_ID, Application_no) Foreign Key (referential attributes): Attributes that define relationships between entities. The attributes of a foreign key in one entity are the attributes of a primary key in another entity; e.g., Department ID is the primary key of Department and Department ID is a foreign key of Employee defining the relationship "Employee works for Department" Key Attribute 12

Relationships Relationships: A relationship is a connection between entity classes. The cardinality of a relationship indicates the number of instances in entity class E1 that can or must be associated with instances in entity class E2. –One-One Relationship: (citizen – passport, –One-Many Relationship: (student-Advisor, Customer-Order) –Many- Many Relationship: (e.g. Student- Organization, Order-Products) –Recursive Relationships: A relationship in which the same entity participates more than once. 13

Binary relationship: between two entity sets –e.g., binary relationship set STUDY between STUDENT and COURSE Ternary relationship: among three entity sets –e.g., ternary relationship STUDY could be ternary among STUDENT, COURSE and TEACHER –A relationship may have attributes e.g., attribute GRADE and SEMESTER for STUDY Relationships, (cont.) 14

Optional And Mandatory 15

Optional And Mandatory, (cont.) 16

ERD Notations Rectangles represent ENTITY CLASSES Circles represent ATTRIBUTES Diamonds represent RELATIONSHIPS Arcs connect entities to relationships. Arcs are also used to connect attributes to entities. Some styles of entity-relationship diagrams use arrows and double arrows to indicate the one and the many in relationships. Underline - Key attributes of entities are underlined. 17

Summary Of ERD Notations 18

Example

Add Some Attributes To Entities

Exercise A company is organized into departments. Each department has a unique name, a unique number, and a particular employee who manages the department. A department may have several locations. A department may control a number of projects, each of which has a unique name, a unique number, and a single location. A project must controlled by department. We store employee’s name, social security number, address, salary, gender and birth date. 21

An employee must be assigned to one department and must work on one or more projects, which are not necessarily controlled by the same department. We keep track of the number of hours per week that an employee works on each project. We also keep track of the direct supervisor of each employee. We want to keep track of the dependents of each employee for insurance purposes. We keep each dependent’s first name, gender, birth date and relationship to that employee. Exercise, (cont.) 22

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ERD Mapping to Tables

ER-to-Relational Mapping Step 1: Mapping of Regular Entity Types Step 2: Mapping of Weak Entity Types Step 3: Mapping of Binary 1:1 Relation Types Step 4: Mapping of Binary 1:N Relationship Types. Step 5: Mapping of Binary M:N Relationship Types. Step 6: Mapping of Multi-valued attributes. Step 7: Mapping of N-ary Relationship Types. 25

Step 1: Mapping of Regular Entity Types Create table for each regular (strong) entity type. Choose one of key attributes to be the primary key. 26

Step 2: Mapping of Weak Entity Types Create table for each weak entity. Add foreign key that correspond to the owner entity type. Choose the primary key : ( FK + weak entity Partial PK if any). 27

Step 3: Mapping of Binary 1:1 Relation Types 1.Merged two tables if both sides are Mandatory. 2.Add FK into table with the Mandatory relationship to represent optional side. 3.Create a third table with just the keys from the two tables in addition to the two table if both sides are optional. 28

Step 4: Mapping of Binary 1:N Relationship Types If the N-side is mandatory, add FK to N-side table Add any simple attributes of relationship as column to N-side table. If the N-side is optional, create a third table The of the new table consists of a concatenation of the keys of the related entities. Include any attributes that were in the relationship. 29

Step 5: Mapping of Binary M:N Relationship Types Create a new third table Add FKs to the new table for both parent tables Add simple attributes of relationship to the new table if any. 30

Step 6: Mapping of Multi-valued attributes Create new table for each multi-valued attribute Table will include two columns: one for multi-valued attribute + FK column. 31

Step 7: Mapping of N-ary Relationship Types If n > 2 then : Create a new third table Add FKs to the new table for all parent tables Add simple attributes of relationship to the new table if any. 32

Mapping of N-ary Relationship (Example) 33

Referential Integrity Referential Integrity requires that: –The columns of a foreign key must match in type the columns of the primary key in the referenced table. –The values of the foreign key columns in each row of the referencing table must match the values of the corresponding primary key columns for a row in the referenced table. 34

Referential Integrity, (cont.) 35

No Action –only primary keys with no matching foreign keys can be deleted/Updated –the change to the referenced (primary key) table is not performed. Cascade where the foreign key in the case matching is deleted/updated. –For update (the primary key column values have been modified), the corresponding foreign key columns for referencing rows are set to the new values. –For delete (the primary key row is deleted), the referencing rows (foreign key) are deleted Referential Integrity, (cont.) 36

SET NULL –All matching foreign keys are set to null, and delete/update then takes place in other relation. SET Default –all matching foreign keys are set to default value, and delete/update then takes place in other relation. Referential Integrity, (cont.) 37

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Mapping Result 39

SQL Basics

 Create Table  Drop Table  Alter Table 41 Data Definition Language (DDL)

Create Table The Create table statement is used to create a table in a database and to add constraints. –Constraints: NOT NULL UNIQUE PRIMARY KEY FOREIGN KEY CHECK DEFAULT

CREATE TABLE person( id int, name varchar(50) not null, varchar(50), age int default 18, Dept_ID int, primary key(id), check(age>17), unique( ), foreign key (Dept_ID) REFERENCES Department(Dept_ID)) Create Table Example

Drop Table Used to remove a relation (base table) and its definition The relation can no longer be used in queries, updates, or any other commands since its description no longer exists Example: DROP TABLE DEPENDENT;

Alter Table Used to modify the table design like add a column, modify a column or delete a column. Examples: ALTER TABLE EMPLOYEE ADD JOB VARCHAR(12) ALTER TABLE EMPLOYEE ALTER COLUMN JOB VARCHAR(50) ALTER TABLE EMPLOYEE DROP COLUMN JOB

 SELECT o Extracts data from a database  INSERT INTO o Inserts new data into a database  UPDATE o Updates data in a database  DELETE o Deletes data from a database 46 Data Manipulation Language (DML)

INSERT INTO Statement First form: It doesn't specify the column names where the data will be inserted, only their values. –The previous form the attribute values should be listed in the same order as the attributes were specified in table. 47 INSERT INTO Employee VALUES ( 4,'Ahmed', ‘Ali', , ' ', '15 Ali fahmy St.Giza‘, ‘M’,1300,223344,10 )

INSERT INTO Statement, (cont.) Second form: It specifies both the column names and the values to be inserted 48 INSERT INTO Employee ( SSN, Lname, fname ) VALUES ( 5, ‘Ahmed', ‘Ali')

To insert a new row into table with identity value, we will not have to specify a value for the identity column (a unique value will be added automatically): The Result: insert into Department values('DP2','56733') insert into Department(Dname,MGRSSN) values('DP2','56733') INSERT INTO Statement, (cont.)

UPDATE Statement The UPDATE statement is used to update existing records in a table. SQL Syntax –UPDATE table_name SET column1=value, column2=value2,... WHERE some_column=some_value Note: The WHERE clause specifies which record or records that should be updated. If you omit the WHERE clause, all records will be updated! UPDATE Person SET Address='18 Abaas El 3akaad St. Nasr City.Cairo', City='Cairo' WHERE Lname=‘Amr' AND Fname='Ali'

DELETE Statement The DELETE statement is used to delete rows in a table. 51 delete from Employee where Lname='Brown’

SELECT Statement Basic form of the SQL SELECT statement is called a mapping or a SELECT-FROM-WHERE block SELECT FROM WHERE – is a list of attribute names whose values are to be retrieved by the query – is a list of the relation names required to process the query – is a conditional (Boolean) expression that identifies the tuples to be retrieved by the query

Or: SELECT Statement Examples SELECT Lname,Fname FROM Person SELECT Person.Lname, Person.Fname FROM Person SELECT * FROM Person WHERE City='Sandnes'

LIKE Operator Example SELECT * FROM Person WHERE City LIKE 's%' SELECT * FROM Person WHERE City LIKE '%s' SELECT * FROM Person WHERE City LIKE '_andnes' Used to represent one character

SQL AND & OR Operators AND operator displays records when all conditions are true. OR operator displays records when any condition is true.

SQL AND & OR Operators Example

IN Operator Example Retrieve data of all employees whose social security numbers number is , or –Query : SELECT * FROM Employee WHERE SSN IN (112233,512463)

IN Operator Example Retrieve data of all employees whose social security numbers number is not , or –Query : SELECT * FROM Employee WHERE SSN not IN (112233,512463)

The BETWEEN Operator The BETWEEN operator is used in a WHERE clause to select a range of data between two values. Retrieve the employees with salary between 1000 and 2000 –Query : SELECT * FROM EMPLOYEE WHERE SALARY BETWEEN 1000 AND 2000

NULLS IN SQL QUERIES SQL allows queries that check if a value is NULL. SQL uses IS or IS NOT to compare Nulls. Retrieve the names of all employees who do not have supervisors. –Query : SELECT FNAME, LNAME FROM EMPLOYEE WHERESUPERSSN IS NULL

DISTINCT Keyword The keyword DISTINCT is used to eliminate duplicate tuples in a query result.

SQL Alias It used to give table or column(s) another name.

If we want to display column called full name that concatenate between first name and last name. SQL Alias Example

When we want to concatenate between columns, all columns should have the same data type. If we want to concatenate between two columns that have different data type, use convert() function that convert from data type to another. Note

SQL TOP Clause It is used to specify the number of records to return. Retrieve the first two record from EMPLOYEE table

ORDER BY Keyword Ordering of rows displayed Opposite order is given by DESC

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