Database Basics CPSC 4670/5670

2 Purpose of a Database The purpose of a database is to keep track of things Unlike a list or spreadsheet, a database may store information that is more complicated than a simple list

3 Database Systems The four components of a database system are: Users Database Application Database Management System (DBMS) Database

4 Users, Database A user of a database system will Use a database application to track things Use forms to enter, read, delete and query data Produce reports A database is a self-describing collection of related records Self-describing The database itself contains the definition of its structure Metadata is data describing the structure of the database data Tables within a relational database are related to each other

5 Database Management System (DBMS) A database management system (DBMS) serves as an intermediary between database applications and the database The DBMS manages and controls database activities The DBMS creates, processes and administers the databases it controls Create databases Create tables Create supporting structures Read database data Modify database data (insert, update, delete) Maintain database structures Enforce rules i.e., Referential Integrity Constraints Control concurrency Provide security Perform backup and recovery

6 Database Applications A database application is a set of one or more computer programs that serves as an intermediary between the user and the DBMS A database application Create and process forms Process user queries Create and process reports Execute application logic Control database applications

7 Desktop Database Systems Desktop database systems typically: Have one application Have only a few tables Are simple in design Involve only one computer Support one user at a time

8 Organizational Database Systems Organizational database systems typically: Support several users simultaneously Include more than one application Involve multiple computers Are complex in design Have many tables Have many databases

9 Commercial DBMS Products Example Desktop DBMS Products Microsoft Access Example Organizational DBMS Products Oracle’s Oracle Microsoft’s SQL Server IBM’s DB2 InterSystems Caché®

The Relational Model

11 Relational Databases Relational databases are designed to address many of the information complexity issues A relational database stores information in tables. Each informational topic is stored in its own table. In essence, a relational database will break-up a list into several parts. One part for each theme in the list. A Project List would be divided into a CUSTOMER Table, a PROJECT Table, and a PROJECT_MANAGER Table

12 Entity An entity is something of importance to a user that needs to be represented in a database An entity represents one theme or topic

13 Relation A relation is a two-dimensional table that has specific characteristics The table dimensions, like a matrix, consist of rows and columns

14 Characteristics of a Relation Rows contain data about an entity Columns contain data about attributes of the entity Cells of the table hold a single value All entries in a column are of the same kind Each column has a unique name The order of the columns is unimportant The order of the rows is unimportant No two rows may be identical

15 A Sample Relation EmployeeNumberFirstNameLastName 100MaryAbermany 101JerryCaldera 104AleaCopley 107MuruganJacksoni

16 A Nonrelation Example EmployeeNumberPhoneLastName , Abermany Caldera Copley Jacksoni Cells of the table hold multiple values

17 EmployeeNumberPhoneLastName Abermany Caldera Copley Abermany Jacksoni No two rows may be identical A Nonrelation Example

18 Terminology TableRowColumn File or Data fileRecordField RelationTupleAttribute Synonyms…

19 A Key and Uniqueness of Keys A key is one (or more) columns of a relation that is (are) used to identify a row Unique KeyNon-unique Key Data value is unique for each row. Consequently, the key will uniquely identify a row. Data value may be shared among several rows. Consequently, the key will identify a set of rows.

20 A Composite Key A composite key is a key that contains two or more attributes For a key to be unique, often it must become a composite key For example, To identify a family member, you need to know a FamilyID, a FirstName, and a Suffix (e.g., Jr.) The composite key is: (FamilyID, FirstName, Suffix) One needs to know the value of all three columns to uniquely identify an individual

21 A Candidate and Primary Key A candidate key is called “candidate” because it is a candidate to become the primary key A candidate key is a unique key A primary key is a candidate key chosen to be the main key for the relation If you know the value of the primary key, you will be able to uniquely identify a single row

22 Relationships Between Tables A table may be related to other tables For example An Employee works in a Department A Manager controls a Project To preserve relationships, you may need to create a foreign key A foreign key is a primary key from one table placed into another table The key is called a foreign key in the table that received the key

23 Foreign Key Example Project ProjID ProjName MgrID Manager MgrID MgrName Foreign Key Primary Key

24 Department DeptID DeptName Location Employee EmpID DeptID EmpName Foreign Key Primary Key Foreign Key Example

25 Referential Integrity Referential integrity states that every value of a foreign key must match a value of an existing primary key For example (see previous slide) If EmpID = 4 in EMPLOYEE has a DeptID = 7 (a foreign key), a Department with DeptID = 7 must exist in DEPARTMENT

26 Referential Integrity Another perspective… The value of the Foreign Key EmployeeID in EQUIPMENT must exist in The values of the Primary Key EmployeeID in EMPLOYEE

27 A Surrogate Key A Surrogate Key is a unique, numeric value that is added to a relation to serve as the Primary Key Surrogate Key values have no meaning to users and are usually hidden in forms, queries and reports A Surrogate Key is often used in place of a composite primary key

28 Surrogate Key Example If the Family Member Primary Key is FamilyID, FirstName, Suffix, it would be easier to append and use a surrogate key of FamMemberID FamilyID, FirstName and Suffix remain in the relation Referential Integrity: Use… (FamMemberID) in School must exist in (FamMemberID) in FamilyMember Instead of: (FamilyID, FirstName, Suffix) in School must exist in (FamilyID, FirstName, Suffix) in FamilyMember

29 Functional Dependency A relationship between attributes in which one attribute (or group of attributes) determines the value of another attribute in the same table Illustration… The price of one cookie can determine the price of a box of 12 cookies (CookiePrice, Qty)BoxPrice

30 Determinants The attribute (or attributes) that we use as the starting point (the variable on the left side of the equation) is called a determinant (CookiePrice, Qty)BoxPrice Determinant

31 Candidate/Primary Keys and Functional Dependency By definition… A candidate key of a relation will functionally determine all other attributes in the row Likewise, by definition… A primary key of a relation will functionally determine all other attributes in the row

32 Primary Key and Functional Dependency Example (EmployeeID) (EmpLastName, EmpPhone) (ProjectID)(ProjectName, StartDate)

33 Normalization Normalization is a process of analyzing a relation to ensure that it is well- formed More specifically, if a relation is normalized (well-formed), rows can be inserted, deleted, or modified without creating update anomalies

34 Normalization Principles Relational design principles for normalized relations: To be a well-formed relation, every determinant must be a candidate key Any relation that is not well formed should be broken into two or more well-formed relations.

35 Normalization Example (StudentID) (StudentName, DormName, DormCost) (DormName)(DormCost) However, if… (StudentID) (StudentName, DormName) (DormName)(DormCost) Then DormCost should be placed into its own relation, resulting in the relations:

36 Normalization Example (AttorneyID, ClientID) (ClientName, MeetingDate, Duration) (ClientID)(ClientName) However, if… (ClientID) (ClientName) (AttorneyID, ClientID) (MeetingDate, Duration) Then ClientName should be placed into its own relation, resulting in the relations:

37 Structured Query Language (SQL)

38 Structured Query Language Acronym: SQL Pronounced as “S-Q-L” Also pronounced as “Sequel” Originally developed by IBM as the SEQUEL language in the 1970s SQL-92 is an ANSI national standard adopted in 1992

39 SQL Defined SQL is an international standard for creating, processing and querying database and their tables. SQL is comprised of: A data definition language (DDL) Used to define database structures A data manipulation language (DML) Data definition and updating Data retrieval (Queries)

40 SQL for Data Definition The SQL data definition statements include CREATE To create database objects ALTER To modify the structure and/or characteristics of database objects DROP To delete database objects

41 SQL for Data Definition: CREATE Creating database tables The SQL CREATE TABLE statement CREATE TABLE Employee( EmpID Integer Primary Key, EmpName Char(25) Not Null );

42 SQL for Data Definition: CREATE with CONSTRAINT Creating database tables with PRIMARY KEY constraints The SQL CREATE TABLE statement The SQL CONSTRAINT keyword CREATE TABLE Employee( EmpID Integer Not Null, EmpName Char(25) Not Null CONSTRAINT EmpPK PRIMARY KEY (EmpID) );

43 SQL for Data Definition: CREATE with CONSTRAINT Creating database tables with composite primary keys using PRIMARY KEY constraints The SQL CREATE TABLE statement The SQL CONSTRAINT keyword CREATE TABLE Emp_Skill ( EmpID Integer Not Null, SkillID Integer Not Null, SkillLevel Integer, CONSTRAINT EmpSkillPK PRIMARY KEY (EmpID, SkillID) );

44 SQL for Data Definition: CREATE with CONSTRAINT Creating database tables using PRIMARY KEY and FOREIGN KEY constraints The SQL CREATE TABLE statement The SQL CONSTRAINT keyword CREATE TABLE Emp_Skill ( EmpIDInteger Not Null, SkillID Integer Not Null, SkillLevelInteger, CONSTRAINTEmpSkillPK PRIMARY KEY (EmpID, SkillID), CONSTRAINTEmpFKFOREIGN KEY EmpIDREFERENCES Employee (EmpID), CONSTRAINT SkillFKFOREIGN KEY SkillIDREFERENCES Skill (SkillID) );

45 SQL for Data Definition: CREATE with CONSTRAINT Creating database tables using PRIMARY KEY and FOREIGN KEY constraints The SQL CREATE TABLE statement The SQL CONSTRAINT keyword ON UPDATE CASCADE and ON DELETE CASCADE CREATE TABLE Emp_Skill ( EmpIDInteger Not Null, SkillID Integer Not Null, SkillLevel Integer, CONSTRAINT EmpSkillPK PRIMARY KEY (EmpID, SkillID), CONSTRAINT EmpFKFOREIGN KEY (EmpID) REFERENCES Employee (EmpID) ON DELETE CASCADE, CONSTRAINT SkillFKFOREIGN KEY (SkillID) REFERENCES Skill (SkillID) ON UPDATE CASCADE ); When the row of EmpID (primary key) in Employee TABLE is deleted, the EmpFK (foreign key) is deleted also.

46 Deleting Database Objects: DROP To remove unwanted database objects from the database, use the SQL DROP statement Warning… The DROP statement will permanently remove the object and all data DROP TABLE Employee;

47 Removing a Constraint: ALTER & DROP To change the constraints on existing tables, you may need to remove the existing constraints before adding new constraints ALTER TABLE Employee DROP CONSTRAINT EmpFK;

48 SQL for Data Retrieval (Queries) SELECT is the best known SQL statement SELECT will retrieve information from the database that matches the specified criteria SELECT EmpName FROM Emp;

49 The Results of a Query is a Relation A query pulls information from one or more relations and creates (temporarily) a new relation This allows for a query to: Create a new relation Feed information to another query (as a “sub-query”)

50 Displaying All Columns: * To show all of the column values for the rows that match the specified criteria, use an * SELECT * FROM Emp; Showing a Row Only Once: DISTINCT A qualifier may be added to the SELECT statement to inhibit duplicate rows from displaying SELECT DISTINCT DeptID FROM Emp;

51 Specifying Search Criteria: WHERE The WHERE clause stipulates the matching criteria for the record that are to be displayed SELECT EmpName FROM Emp WHERE DeptID = 15;

52 Match Criteria The WHERE clause match criteria may include Equals “=“ Not Equals “<>” Greater than “>” Less than “<“ Greater than or Equal to “>=“ Less than or Equal to “<=“

53 Match Operators Multiple matching criteria may be specified using AND Representing an intersection of the data sets OR Representing a union of the data sets SELECT EmpName FROM Emp WHERE DeptID < 7 OR DeptID > 12;

54 A List of Values The WHERE clause may specify that a particular column value must be included in a list of values SELECT EmpName FROM Emp WHERE DeptID IN (4, 8, 9);

55 The Logical NOT Operator Any criteria statement may be preceded by a NOT operator which is to say that all information will be shown except that information matching the specified criteria SELECTEmpName FROMEmp WHEREDeptID NOT IN (4, 8, 9);

56 Finding Data Matching a Range of Values: BETWEEN SQL provides a BETWEEN statement that allows a user to specify a minimum and maximum value on one line SELECTEmpName FROMEmp WHERESalaryCode BETWEEN 10 AND 45;

57 Allowing for Wildcard Searches: LIKE Sometimes it may be advantageous to find rows matching a string value using wildcards Single character wildcard character is an underscore (_) Multiple character wildcard character is a percent sign (%)

58 Wildcard Search Examples SELECT EmpID FROM Emp WHERE EmpName LIKE ‘Kr%’; SELECT EmpID FROM Emp WHERE Phone LIKE ‘616-___-____’; 3 underscores

59 Sorting the Results: ORDER BY The results may be sorted using the ORDER BY clause SELECT * FROM Emp ORDER BY EmpName;

60 Built-in SQL Functions SQL provides several built-in functions COUNT Counts the number of rows that match the specified criteria MIN Finds the minimum value for a specific column for those rows matching the criteria MAX Finds the maximum value for a specific column for those rows matching the criteria

61 Built-in SQL Functions (continued) SUM Calculates the sum for a specific column for those rows matching the criteria AVG Calculates the numerical average of a specific column for those rows matching the criteria

62 Built-in Function Examples SELECT COUNT(DISTINCT DeptID) FROM Emp; SELECT MIN(Hours), MAX(Hours), AVG(Hours) FROM Project WHERE ProjID > 7;

63 Providing Subtotals: GROUP BY Subtotals may be calculated by using the GROUP BY clause SELECT DeptID, COUNT(*) FROM Emp GROUP BY DeptID HAVING Count(*) > 3;

64 Retrieving Information from Multiple Tables SubQueries As stated earlier, the result of a query is a relation. As a result, a query may feed another query. This is called a subquery Joins Another way of combining data is by using a Join Join [also called an Inner Join] Left Outer Join Right Outer Join

65 Subquery SELECT EmpName FROM Emp WHERE DeptID in (SELECT DeptID FROM Department WHERE DeptName LIKE ‘Accounts%’);

66 Join SELECT EmpName FROM Emp, Department WHERE Emp.DeptID = Department.DeptID AND Department.DeptName LIKE ‘Account%’;

67 Modifying Data using SQL Insert Will add a new row in a table Update Will update the data in a table that matches the specified criteria Delete Will delete the data in a table that matches the specified criteria

68 Adding Data: INSERT To add a row to an existing table, use the INSERT statement INSERT INTO Emp VALUES (91, ‘Smither’, 12); INSERT INTO Emp (EmpID, SalaryCode) VALUES (62, 11);

69 Changing Data Values: UPDATE To change the data values in an existing row (or set of rows) use the Update statement UPDATE Emp SET Phone =‘ ’ WHERE EmpID = 29; UPDATE Emp SET DeptID = 44 WHERE EmpName LIKE ‘Kr%’;

70 Deleting Data: DELETE To delete a row or set of rows from a table using the DELETE statement DELETE FROM Emp WHERE EmpID = 29; DELETE FROM Emp WHERE EmpName LIKE ‘Kr%’;

71 Movie(title, length) SELECT title AS name, length * AS lengthInHours

72 SELECT name FROM MovieExec, Movies, StarIn WHERE cert# = producerC# AND title = movieTitle AND year = movieYear AND starName = ‘Harrison Ford’ MovieExec(name, address, cert#, netWorth) Movies(title, year, length, genre, studioName, producerC#) StarsIn(movieTitle, movieYear, starName)

73 Movies(title, year, length, genre, studioName, producerC#) MovieExec(name, address, cert#, netWorth) StarsIn(movieTitle, movieYear, starName) SELECT name FROM MovieExec WHERE cert# IN (SELECT producerC# FROM Movies WHERE (title, year) IN (SELECT movieTitle, MovieYear) FROM StartsIn WHERE starName = ‘Harrison Ford’) );