SQL for Data Retrieval

Save your SQL Scripts

• When working with SQL Management Studio, you should keep saving your scripts as a .sql file to somewhere in your local computer (e.g., Desktop)

• For assignment 3, you should submit a single .sql file (not word or pdf file!) to ANGEL which contains all your scripts

Queries

• SELECT is the best known SQL statement• SELECT will retrieve information from the

database that matches the specified criteria using the SELECT / FROM / WHERE framework

SELECT ColumnName

FROM TableWHERE Condition;

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Running Example

Data Preparation

• Login to SQL server using your account• Select your database

– Your database name is your PSU ID– Alternatively, you can add one statement at the first line of

each script: USE [your PSU ID];

• Download three SQL script files from course schedule page and open them in SQL Server Management Studio.1. SQL-Delete-Tables.sql2. SQL-Create-Tables.sql3. SQL-Insert-Data.sql

• Execute scripts (1 2 3).

View the Database Diagram

• Right click “Database Diagrams”• Click “New Database Diagrams”• Select all tables

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Diagram View

SQL for Data Retrieval: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 a query to: – Create a new relation– Feed information to another query (as a “sub-

query”)

SQL for Data Retrieval:Displaying Specified Columns

• The following SQL statement queries three of the six columns of the PROJECT table:

SELECT ProjectName, Department, MaxHoursFROM PROJECT;

SQL for Data Retrieval:Displaying All Columns

• To show all of the column values for the rows that match the specified criteria, use an asterisk ( * )

SELECT * FROM PROJECT;

SQL for Data Retrieval:Showing Each Row Only Once

• The DISTINCT keyword may be added to the SELECT statement to inhibit duplicate rows from displaying

SELECT DepartmentFROM EMPLOYEE;

SELECT DISTINCT DepartmentFROM EMPLOYEE;

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Exercise 1

• Q1. Show all the FirstName and LastName of employees

• Q2. Show all distinct Firstname of employees

SQL for Data Retrieval:Specifying Search Criteria

• The WHERE clause stipulates the matching criteria for the record that are to be displayed

SELECT FirstName, LastNameFROM EMPLOYEEWHERE Department = 'Administration‘

SELECT *FROM PROJECTWHERE MaxHours > 135

SQL for Data Retrieval: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 “<=“

SQL for Data Retrieval: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

SQL for Data Retrieval:Operator Examples

• Find the employee numbers of those employees who worked less than 20 hours or more than 50 hours on their assignments.

SELECT EmployeeNumberFROM ASSIGNMENTWHERE HoursWorked < 20

OR HoursWorked > 50;

• Find the projects from Finance department with MaxHours larger than 135.

SELECT *FROM PROJECTWHERE Department = 'Finance'

AND MaxHours > 135;

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Exercise 2

• Q1. Show all the employees with FirstName as George or Department is Finance

• Q2. Show all the employee with Department is Finance or Accounting or Marketing

SQL for Data Retrieval:A List of Values

• The WHERE clause may include the IN keyword to specify that a particular column value must be included in a list of values

SELECT LastNameFROM EMPLOYEEWHERE Department IN ('Finance', 'Legal',

'Info Systems');

SQL for Data Retrieval: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

SELECT LastNameFROM EMPLOYEEWHERE Department NOT IN ('Finance',

'Legal', 'Info Systems');

SQL for Data Retrieval:Finding Data in a Range of Values

• SQL provides a BETWEEN statement that allows a user to specify a minimum and maximum value on one line

SELECT EmployeeNumberFROM ASSIGNMENTWHERE HoursWorked BETWEEN 20 and 50

SQL for Data Retrieval:IS NULL Keyword

• Find all rows which have null values for an specified attribute:

SELECT FirstName, LastName, Phone, DepartmentFROM EMPLOYEEWHERE Phone IS NULL;

SELECT FirstName, LastName, Phone, DepartmentFROM EMPLOYEEWHERE Phone = NULL;

Bad Query!

SQL for Data Retrieval:Allowing for Wildcard Searches

• The SQL LIKE keyword allow searches on partial data values

• LIKE can be paired with wildcards to find rows matching a string value– Multiple character wildcard character is a percent

sign (%)– Single character wildcard character is an

underscore (_)

SQL for Data Retrieval:Wildcard Search Examples

• Find all employees whose last name starts with “J”.

SELECT *FROM EMPLOYEEWHERE LastName LIKE 'J%';

• Find all employees whose phone number ends with 10.

SELECT *FROM EMPLOYEEWHERE Phone LIKE '___-___-__10';

Exercise 3

• Q1. Find employees whose FirstName ends with “y” and has 4 letters in total

• Q2. Find employees whose FirstName starts with letter “R” and ends with letter “d”

• Q3. Find employees whose FirstName has “a” as the 3rd letter and ends with letter “r”