Upload
others
View
11
Download
0
Embed Size (px)
Citation preview
6
1
Chapter 6
Introduction to Structured QueryLanguage (SQL)
Database Systems:Design, Implementation, and Management,
Sixth Edition, Rob and Coronel
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
2
In this chapter, you will learn:
•The basic commands and functions of SQL
•How to use SQL for data administration (tocreate tables, indexes, and views)
•How to use SQL for data manipulation (to add,modify, delete, and retrieve data)
•How to use SQL to query a database to extractuseful information
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
3
Introduction to SQL
•SQL functions fit into two broad categories:•Data definition language
–SQL includes commands to create•Database objects such as tables, indexes, and
views•Commands to define access rights to those
database objects
•Data manipulation language–Includes commands to insert, update, delete,
and retrieve data within the database tables
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
4
Introduction to SQL (continued)
•SQL is relatively easy to learn
•Basic command set has a vocabulary of lessthan 100 words
•Nonprocedural language
•American National Standards Institute (ANSI)prescribes a standard SQL
•Several SQL dialects exist
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
5
SQL Data Definition Commands
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
6
Data Manipulation Commands
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
7
Data Definition Commands
•Examine the simple database model and thedatabase tables that will form the basis for themany SQL examples
•Understand the data environment
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
8
The Database Model
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
9
Creating the Database
•Two tasks must be completed–create the database structure
–create the tables that will hold the end-userdata
•First task–RDBMS creates the physical files that will hold
the database
–Tends to differ substantially from one RDBMSto another
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
10
The Database Schema
•Authentication–Process through which the DBMS verifies that
only registered users are able to access thedatabase
–Log on to the RDBMS using a user ID and apassword created by the databaseadministrator
•Schema–Group of database objects—such as tables
and indexes—that are related to each other
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
11
Data Types
•Data type selection is usually dictated by thenature of the data and by the intended use
•Pay close attention to the expected use ofattributes for sorting and data retrievalpurposes
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
12
Some Common SQL Data Types
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
13
Creating Table Structures
•Use one line per column (attribute) definition•Use spaces to line up the attribute characteristics and
constraints•Table and attribute names are capitalized•NOT NULL specification•UNIQUE specification•Primary key attributes contain both a NOT NULL and a
UNIQUE specification•RDBMS will automatically enforce referential integrity
for foreign keys•Command sequence ends with a semicolon
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
14
Other SQL Constraints
•NOT NULL constraint
–Ensures that a column does not accept nulls
•UNIQUE constraint
–Ensures that all values in a column are unique
•DEFAULT constraint
–Assigns a value to an attribute when a new row isadded to a table
•CHECK constraint
–Validates data when an attribute value is entered
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
15
SQL Indexes•When a primary key is declared, DBMS
automatically creates a unique index
•Often need additional indexes
•Using the CREATE INDEX command, SQLindexes can be created on the basis of anyselected attribute
•Composite index
–Index based on two or more attributes
–Often used to prevent data duplication
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
16
A Duplicated TEST Record
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
17
Data Manipulation Commands
•Adding table rows
•Saving table changes
•Listing table rows
•Updating table rows
•Restoring table contents
•Deleting table rows
•Inserting table rows with a select subquery
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
18
Common SQL Data ManipulationCommands
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
19
A Data View and Entry Form
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
20
Saving Table Changes
•Changes made to table contents are notphysically saved on disk until–Database is closed
–Program is closed
–COMMIT command is used
•Syntax–COMMIT [WORK]
•Will permanently save any changes made toany table in the database
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
21
Listing Table Rows
•SELECT–Used to list contents of table
•Syntax–SELECT columnlist
FROM tablename
•Columnlist represents one or more attributes,separated by commas
•Asterisk can be used as wildcard character tolist all attributes
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
22
Updating Table Rows
•UPDATE
–Modify data in a table
•Syntax
–UPDATE tablenameSET columnname = expression [, columname= expression][WHERE conditionlist];
•If more than one attribute is to be updated inthe row, separate corrections with commas
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
23
Restoring Table Contents•ROLLBACK
–Used restore the database to its previouscondition
–Only applicable if COMMIT command has notbeen used to permanently store the changesin the database
•Syntax–ROLLBACK;
•COMMIT and ROLLBACK only work withdata manipulation commands that are used toadd, modify, or delete table rows
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
24
Deleting Table Rows
•DELETE
–Deletes a table row
•Syntax
–DELETE FROM tablename[WHERE conditionlist ];
•WHERE condition is optional
•If WHERE condition is not specified, all rowsfrom the specified table will be deleted
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
25
Inserting Table Rows with a SelectSubquery
•INSERT–Inserts multiple rows from another table
(source)–Uses SELECT subquery
•Query that is embedded (or nested) insideanother query
•Executed first
•Syntax–INSERT INTO tablename SELECT columnlist
FROM tablename
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
26
Selecting Rows with ConditionalRestrictions
•Select partial table contents by placingrestrictions on rows to be included in output
–Add conditional restrictions to the SELECTstatement, using WHERE clause
•Syntax
–SELECT columnlistFROM tablelist[ WHERE conditionlist ] ;
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
27
Selected PRODUCT Table Attributes forVENDOR Code 21344
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
28
The Microsoft Access QBE and its SQL
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
29
Comparison Operators
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
30
Selected PRODUCT Table Attributes forVENDOR Codes Other than 21344
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
31
Selected PRODUCT Table Attributeswith a P_PRICE Restriction
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
32
Selected PRODUCT Table Attributes:The ASCII Code Effect
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
33
Selected PRODUCT Table Attributes:Date Restriction
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
34
SELECT Statementwith a Computed Column
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
35
SELECT Statement with a ComputedColumn and an Alias
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
36
Arithmetic Operators:The Rule of Precedence
•Perform operations within parentheses
•Perform power operations
•Perform multiplications and divisions
•Perform additions and subtractions
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
37
Selected PRODUCT Table Attributes:The Logical OR
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
38
Selected PRODUCT Table Attributes:The Logical AND
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
39
Selected PRODUCT Table Attributes:The Logical AND and OR
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
40
Special Operators
•BETWEEN–Used to check whether attribute value is within a
range•IS NULL
–Used to check whether attribute value is null•LIKE
–Used to check whether attribute value matches agiven string pattern
•IN–Used to check whether attribute value matches
any value within a value list•EXISTS
–Used to check if a subquery returns any rows
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
41
Advanced Data Definition Commands
•All changes in the table structure are madeby using the ALTER command
–Followed by a keyword that produces specificchange
–Three options are available
•ADD
•MODIFY
•DROP
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
42
Changing a Column’s Data Type
•ALTER can be used to change data type
•Some RDBMSs (such as Oracle) do notpermit changes to data types unless thecolumn to be changed is empty
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
43
Changing a Column’s DataCharacteristics
•Use ALTER to change data characteristics
•If the column to be changed already containsdata, changes in the column’s characteristicsare permitted if those changes do not alterthe data type
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
44
Adding or Dropping a Column
•Use ALTER to add a column
–Do not include the NOT NULL clause for newcolumn
•Use ALTER to drop a column
–Some RDBMSs impose restrictions on thedeletion of an attribute
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
45
The Effect of Data Entry into the NewP_SALECODE Column
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
46
Update of the P_SALECODE Column inMultiple Data Rows
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
47
The Effect of Multiple Data Updates in thePRODUCT Table (MS Access)
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
48
Copying Parts of Tables
•SQL permits copying contents of selectedtable columns so that the data need not bereentered manually into newly created table(s)
•First create the PART table structure
•Next add rows to new PART table usingPRODUCT table rows
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
49
PART Attributes Copiedfrom the PRODUCT Table
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
50
Advanced Select Queries
•SQL provides useful functions
–Count
–Find minimum and maximum values
–Calculate averages
•SQL allows the user to limit queries to onlythose entries having no duplicates or entrieswhose duplicates may be grouped
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
51
Selected PRODUCT Table Attributes:Ordered by (Ascending) P_PRICE
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
52
Partial Listing ofEMPLOYEE Table Contents
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
53
Telephone List Query Results
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
54
A Query Based on Multiple Restrictions
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
55
A Listing of Distinct (Different) V_CODEValues in the PRODUCT Table
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
56
Some Basic SQL Aggregate Functions
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
57
COUNT Function Output Examples
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
58
MAX and MIN Function Output Examples
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
59
The Total Value of All Itemsin the PRODUCT Table
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
60
AVG Function Output Examples
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
61
GROUP BY Clause Output Examples
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
62
Incorrect and Correct Useof the GROUP BY Clause
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
63
An Application of the HAVING Clause
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
64
Virtual Tables: Creating a View
•View is a virtual table based on a SELECTquery–Can contain columns, computed columns,
aliases, and aggregate functions from one ormore tables
•Base tables are tables on which the view isbased
•Create a view by using the CREATE VIEWcommand
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
65
Creating a Virtual Tablewith the CREATE VIEW Command
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
66
Joining Database Tables
•Ability to combine (join) tables on commonattributes is most important distinctionbetween a relational database and otherdatabases
•Join is performed when data are retrievedfrom more than one table at a time
•Join is generally composed of an equalitycomparison between the foreign key and theprimary key of related tables
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
67
Creating Links Through Foreign Keys
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
68
The Results of a Join
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
69
An Ordered and Limited ListingAfter a JOIN
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
70
The Contents of the EMP Table
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
71
Using an Alias to Join a Table to Itself
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
72
The Left Outer Join Results
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
73
The Right Outer Join Results
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
74
Converting an ER Modelinto a Database Structure
•Requires following specific rules that governsuch a conversion
•Decisions made by the designer to governdata integrity are reflected in the foreign keyrules
•Implementation decisions vary according tothe problem being addressed
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
75
The Ch06_Artist Database ERDand Tables
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
76
A Data Dictionaryfor the Ch06_Artist Database
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
77
A Summary of Foreign Key Rules
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
78
Summary•SQL commands can be divided into two
overall categories:–Data definition language commands–Data manipulation language commands
•Basic data definition commands allow you tocreate tables, indexes, and views
•Many SQL constraints can be used withcolumns
•Aggregate functions–Special functions that perform arithmetic
computations over a set of rows
Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel
6
79
Summary (continued)•ORDER BY clause
–Used to sort output of a SELECT statement–Can sort by one or more columns and use
either an ascending or descending order
•Join output of multiple tables with SELECTstatement
•Natural join uses join condition to match onlyrows with equal values in specified columns
•Right outer join and left outer join used toselect rows that have no matching values inother related table