Database Queries and Structured Query Language(SQL)

J.G. ZhengMay 16th 2008

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Overview

SQL Language Query with SQL

All examples can be used with the “AmazonBook” database Download it from the course website

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Introduction/Review

What is SQL Review: Database and DBMS (chapter 1) SQL is a standard language accepted by

relational DBMS to perform database operations

Some facts about SQL SQL 92 is the most commonly supported version English-like (not programming) Case insensitive Venders have different implementations

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Concepts Review

Relational model concepts reviewRelation : TableRow : RecordColumn : Field (Attribute)

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Common Data Types

Numeric INTEGER, SMALLINT DECIMAL(i,j), NUMBER(i,j)

Character/String CHAR(n), VARCHAR(n)

Date DATE, DATETIME

See textbook page 42-43 for data types implemented in Access

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SELECT Statement

SELECT statement retrieves data from database (query) The result is usually another table

We will learn Defining selection criteria Sorting Calculation Grouping

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SELECT Statement Syntax

SELECT Column(s) or other expressionsFROM Table(s)[WHERE …][ORDER BY ColumnName]

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Simple SELECT Statement

Syntax SELECT * (or a list of columns)

FROM TableName Wild card: *

Example SELECT * FROM Books SELECT BookTitle, ListPrice FROM

Books

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Use WHERE Clause

Use WHERE clause to specify selection criteria

Example SELECT * FROM Books

WHERE ListPrice = 29.99 SELECT BookTitle, ListPrice FROM Books

WHERE ListPrice < 20

Comparison Operators “=“, “>”, “<“, “>=“, “<=“, “<>”

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More Comparison Operators

IN (value list) SELECT * FROM Books

WHERE ListPrice IN (19.99, 29.99, 39.99)

BETWEEN min AND max SELECT * FROM Books

WHERE ListPrice BETWEEN 9.99 AND 19.99

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String Pattern Match

Fuzzy query using LIKE _ (underscore): single character wildcard

? in Access % (percentage): multiple character wildcard

* in Access

Example SELECT * FROM Books

WHERE BookTitle LIKE '*information systems*'

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Compound Conditions

Use logical operators to connect multiple conditions

AND: an intersection of the data sets OR: a union of the data sets

Examples SELECT * FROM Books

WHERE ListPrice <= 19.99 AND ListPrice >= 9.99 SELECT * FROM Books

WHERE PubDate=#10/1/2003# OR PubDate=#10/1/2004#

SELECT * from Books WHERE Publisher = 'Que' AND Binding = 'Paperback'

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Sorting

Syntax ORDER BY Column(s) [ASC/DESC]

Examples SELECT * FROM Books

ORDER BY PubDate SELECT * FROM Books

ORDER BY Publisher DESC, PubDate

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Calculation

Calculating columns Calculated columns are not designed directly

into the table Using +, -, *, / with columns and numbers

Example SELECT BookTitle, ListPrice, ListPrice * 0.1 AS

DiscountFROM BooksWHERE ListPrice * 0.1 >= 15

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Built-in Functions

Using these functions to do statistics MIN MAX COUNT AVG SUM

Example SELECT COUNT(*) FROM Books SELECT AVG(ListPrice) FROM Books

WHERE Publisher = 'Prentice Hall'

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Grouping

GROUP BY: doing math with groups SELECT COUNT(*) FROM Books

WHERE Publisher = 'Prentice Hall';SELECT COUNT(*) FROM Books WHERE Publisher = 'The MIT Press';…

Or:SELECT Publisher, COUNT(*) FROM Books GROUP BY Publisher

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A Complete Query

SELECT ISBN, BookTitle, ListPrice, Publisher

FROM BooksWHERE

BookTitle like '*Information Systems*'AND PubDate > #1/1/2002#AND ListPrice < 100

ORDER BY ListPrice

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ExerciseUsing the “AmazonBook” database, use SQL or QBE to answer the following questions.

1. Which book is the most expensive? 2. How many books are under $100 of list price?3. I am looking for a “database” book, no more

than 50 dollars, and published after 1/1/2003; do you have any recommendations? I need the book title and its price.

4. What is the price per page for the books published by Que? List the book title, price, number of pages and price for page, and sort by the price per page, descending

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Good Resources

SQL Online Tutorial http://sqlcourse.com/ http://sqlcourse2.com/