CPS120: Introduction to Computer Science Information Systems: Database Management Nell Dale John Lewis

Session Goals Describe the elements of a database management system Describe the organization of a relational database Establish relationships among elements in a database Write basic SQL statements

Database Management Systems A database can simply be defined as a structured set of data A database management system (DBMS) is a combination of software and data made up of: –Physical database—a collection of files that contain the data –Database engine—software that supports access to and modification of the database contents –Database schema—a specification of the logical structure of the data stored in the database

Database Management Systems Figure 12.6 The elements of a database management system

The Relational Model In a relational DBMS, the data items and the relationships among them are organized into tables –A table is a collection of records –A record is a collection of related fields –Each field of a database table contains a single data value –Each record in a table contains the same fields

A Database Table Figure 12.7 A database table, made up of records and fields

A Second Table A database table containing customer data

Relationships We can use a table to represent a collection of relationships between objects A database table storing current movie rentals

Structured Query Language The Structured Query Language (SQL) is a comprehensive database language for managing relational databases

What is SQL SQL is an ANSI standard language for accessing databases SQL stands for Structured Query Language SQL can execute queries against a database SQL can retrieve data from a database SQL can insert new records in a database SQL can delete records from a database

Some Definitions Database Tables –Databases contain objects called Tables. –Records of data are stored in these tables. Tables are identified by names (like "Persons", "Orders", "Suppliers"). –Tables contain Columns and Rows with data. Rows contain records (like one record for each person). Columns contain data (like First Name, Last Name, Address, and City).

The Select Statement The SELECT statement selects columns of data from a database The tabular result is stored in a result table (called the result set)

SQL Queries With SQL, we can Query a database and have a Result returned in a tabular form. SELECT LastName FROM Persons

Coding Select Statements To select the columns named "LastName" and "FirstName", use a SELECT statement like this: –SELECT LastName,FirstName FROM Persons To select all columns from the "Persons" table, use a * symbol instead of column name like this: –SELECT * FROM Persons

The WHERE Clause To conditionally select data from a table, a WHERE clause can be added to the SELECT statement with the following syntax: –SELECT column FROM table WHERE column condition value

Where-clause Conditions Relations that can be used: =Equal <>Not equal >Greater than <Less than >=Greater than or equal <=Less than or equal BETWEENBetween an inclusive range LIKEWildcard Search

The LIKE Condition The LIKE condition is used to specify a search for a pattern in a column. The syntax is like this: –SELECT column FROM table WHERE column LIKE pattern A "%" sign can be used to define wildcards (missing letters in the pattern) both before and after the pattern.

Sample LIKE Statements Select Persons with a Name Pattern This SQL statement will return persons with a first name that start with an 'O'. –SELECT * FROM Persons WHERE FirstName LIKE 'O%' This SQL statement will return persons with a first name that end with an 'a'. –SELECT * FROM Persons WHERE FirstName LIKE '%a'

AND and OR AND and OR join two or more conditions in a WHERE clause. –The AND operator displays a row if ALL conditions listed are true. –The OR operator displays a row if ANY of the conditions listed are true. SELECT * FROM Persons WHERE FirstName='Paul'AND LastName='Millis'

Between…And The BETWEEN... AND operator selects an inclusive range of data between two values. These values can be numbers, text, or dates. –SELECT column_name FROM table_name WHERE column_name BETWEEN value1 AND value2

SQL Select Distinct The DISTINCT keyword is used to return only distinct (different) values. –SELECT DISTINCT column-name(s) FROM table-name

SQL Order By The ORDER BY clause is used to sort the rows. Example: To display the companies in alphabetical order: –SELECT Company, OrderNumber FROM OrdersORDER BY Company

SQL Data Manipulation SQL includes a syntax to update records with query and update commands

SQL Data Definition The Data Definition Language (DDL) part of SQL permits database tables to be created or deleted, links between tables defined and, and constraints imposed between database tables.