I1100 - Introduction to Computer Science · Database Management Systems •Generally, these...
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Databases Chapter 5 Introduction to Computer Science (I1100) 2018-2019 427
Transcript of I1100 - Introduction to Computer Science · Database Management Systems •Generally, these...
DatabasesChapter 5
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Outline• What is a Database?
• Database Management Systems
• Relational Database Design
• Entity-Relationship Model
• Structured Query Language
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What is a Database?• A database is a collection of data.
• A database could be as simple as a text file with a list of names.
• Or it could be as complex as a large, relational database management system, complete with in-built tools to help you maintain the data.
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Text File• Imagine we have a text file called data.txt, and that the contents look like
this:
• We could also call each row a record. Therefore, we currently have 4 records in our database.
• With a small list like this, a text file may serve our purposes perfectly.
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Database Software• A better option would be to store the data in a database table using
specialized database software, such as Microsoft Access.
Something like this:
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Database Management Systems
• A Database Management System (DBMS), is a software program that enables the creation and management of databases.
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Database Management Systems• Generally, these databases will be more complex than the text file
example. In fact, most of today's database systems are referred to as a Relational Database Management System (RDBMS), because of their ability to store related data across multiple tables.
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Database Management Systems• Some of the more popular relational database
management systems include:� Microsoft Access
� Filemaker
� Microsoft SQL Server
� MySQL
� Oracle
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Database Management Systems• A typical DBMS has users with different rights and permissions who use it
for different purposes. Some users retrieve data and some back it up. The users of a DBMS can be broadly categorized as follows −
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Database Management Systems• Administrators − Administrators maintain the DBMS and are responsible
for administrating the database.
• Designers − Designers are the group of people who actually work on the designing part of the database.
• End Users − End users are those who actually reap the benefits of having a DBMS.
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What is a Table?• In database terms, a table is responsible for storing data in the database.
Database tables consist of rows and columns.
• In the following example, the second row is highlighted:
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What is a Table?• The second column is highlighted. This column has been given a name of
"FirstName":
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What is a Table?• A row contains each record in the table, and the column is responsible for
defining the type of data that goes into each cell.
• Therefore, if we need to add a new person to our table, we would create a new row with the person's details.
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Microsoft Access TutorialQuerying a Database• Queries are one of the things that make databases so powerful.
• A "query" refers to the action of retrieving data from your database.
• For example, you might only want to see how many individuals in your database live in a given city.
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Relational Database Design• Most popular database management systems are relational systems, and are
usually referred to as Relational Database Management Systems (RDBMS). What this means is that their databases can contain multiple tables, some (or all) of which are related to each other.
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Relational Database Design• In this example, the database has 2 tables. Each table serves a specific
purpose.
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Relational Database Design• Using the example, the Individual table can
hold data that is strictly about the individual. The City table can hold a list of all cities. If we want to know which city each individual lives, we could store a "pointer" in the Individual table to that city in the City table.
• This example demonstrates the relationship between the Users table and the City table. The users in the “Users" table live in cities that are defined in the "City" table. Therefore, we can cross-reference each “Users" record with a "City" record.
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How Does This Work?• Firstly, in the City table, each record has a unique identifier. A unique identifier is a value that
is unique to each record. This identifier can be as simple as an incrementing number. So, in our City table, the first record has a number of 1, the second record has a number of 2, and so on.
• Secondly, when entering each user into the Users table, instead of writing out the full city name in that table, we only need to add the city's unique identifier. In this case, the unique identifier is a number, so we enter this number into the "CityId" column of the “Users" table.
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How Does This Work?
• So, by looking at both tables, we can determine that Khanafer lives in Mcharafieh, Chaiblives in Hadath, and both Itani and Damaj live in Msaytbeh. At this stage, nobody in our database lives in Basta or Khalde.
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Structured Query Language• SELECT one or more column_name
FROM table WHERE one or many conditions
• Example: table called CLIENT
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Structured Query Language• SELECT City
FROM Client;
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Structured Query Language• SELECT FirstName, LastName
FROM Client;
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Structured Query Language• SELECT *
FROM Client;
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Structured Query Language• SELECT DISTINCT FirstName
FROM Client;
! 2 times Pierre !!, to solve next slide
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Structured Query Language• SELECT DISTINCT FirstName
FROM Client;
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Structured Query Language
• Find all the clients that live in Paris
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SELECT * FROM Client WHERE City = ‘Paris’;
Structured Query Language
• Fin the maximum salary of clients
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SELECT MAX(Salary) FROM Client;
We can also use MIN, AVG, COUNT, and SUM functions
Structured Query Language
• Count the number of records in the Client table
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SELECT COUNT(*) AS ClientsNumber FROM Client;
Structured Query Language
• SELECT COUNT(FirstName) FROM Client WHERE FirstName=”Mary”;
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Structured Query Language
• SELECT COUNT(DISTINCT FirstName) FROM Client ;
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Structured Query Language
• SELECT SUM(Salary) FROM Client;
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Structured Query Language
• SELECT AVG(Salary) FROM Client WHERE FirstName = ‘Pierre’;
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The query computes the average of salaries for clients having the first name
=”Pierre”, it is (2,000 + 1,500)/2, and the answer is 1,750$.
Structured Query Language• There are many comparison operators that can be written in WHERE such
as :
� equal =,
� different <> or !=,
� greater than >,
� less than <,
� greater or equal >=,
� less than or equal <=,
� IN, BETWEEN, N
� OT BETWEEN,
� LIKE, and
� IS NULL.
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Structured Query Language
• SELECT Id, FirstNameFROM Client WHERE City=’Paris’ OR City=’Nantes’;
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Structured Query Language
• SELECT Id, FirstName, Salary FROM Client WHERE FirstName =’Pierre’ AND Salary> 1500;
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Structured Query Language
• SELECT FirstNameFROM Client WHERE LastName= ‘Dupont’ OR LastName = ‘Durant’ OR LastName= ‘Matrin’;
SELECT FirstName FROM Client WHERE LastName IN (‘Durant’, ‘Dupont’, ‘Martin’);
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Structured Query Language
• SELECT Id, LastName FROM Client WHERE Salary BETWEEN 100 AND 1000;
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Structured Query Language
• SELECT Id, LastName FROM Client WHERE Salary NOT BETWEEN 100 AND 1000;
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Structured Query Language
• SELECT FirstName, LastName FROM Client WHERE LastName LIKE “%D”; => LastName ends with letter D.
• SELECT FirstName, LastName FROM Client WHERE LastName LIKE “D%”; => LastName starts with letter D.
• SELECT FirstName, LastName FROM Client WHERE LastName LIKE “%D%”; => LastName contains letter D.
• SELECT FirstName, LastName FROM Client WHERE LastName LIKE “D%t”; => LastName starts with D and ends with t.
• SELECT FirstName, LastName FROM Client WHERE LastName LIKE “A_C”; => The underscore “_” character will be replaced by any character such as ABC, AEC, etc. It means that the Last name contains exactly 3 characters, the first one is A, the last one is C, and a character.
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