Home > Articles > Web Development

📄 Contents

  1. Sams Teach Yourself SQL in 24 Hours, Third Edition
  2. Table of Contents
  3. Copyright
  4. About the Authors
  5. Acknowledgments
  6. Tell Us What You Think!
  7. Introduction
  8. Part I: A SQL Concepts Overview
  9. Hour 1. Welcome to the World of SQL
  10. SQL Definition and History
  11. SQL Sessions
  12. Types of SQL Commands
  13. An Introduction to the Database Used in This Book
  14. Summary
  15. Q&A
  16. Workshop
  17. Part II: Building Your Database
  18. Hour 2. Defining Data Structures
  19. What Is Data?
  20. Basic Data Types
  21. Summary
  22. Q&A
  23. Workshop
  24. Hour 3. Managing Database Objects
  25. What Are Database Objects?
  26. What Is a Schema?
  27. A Table: The Primary Storage for Data
  28. Integrity Constraints
  29. Summary
  30. Q&A
  31. Workshop
  32. Hour 4. The Normalization Process
  33. Normalizing a Database
  34. Summary
  35. Q&A
  36. Workshop
  37. Hour 5. Manipulating Data
  38. Overview of Data Manipulation
  39. Populating Tables with New Data
  40. Updating Existing Data
  41. Deleting Data from Tables
  42. Summary
  43. Q&A
  44. Workshop
  45. Hour 6. Managing Database Transactions
  46. What Is a Transaction?
  47. What Is Transactional Control?
  48. Transactional Control and Database Performance
  49. Summary
  50. Q&A
  51. Workshop
  52. Part III: Getting Effective Results from Queries
  53. Hour 7. Introduction to the Database Query
  54. What Is a Query?
  55. Introduction to the <tt>SELECT</tt> Statement
  56. Examples of Simple Queries
  57. Summary
  58. Q&amp;A
  59. Workshop
  60. Hour 8. Using Operators to Categorize Data
  61. What Is an Operator in SQL?
  62. Comparison Operators
  63. Logical Operators
  64. Conjunctive Operators
  65. Negating Conditions with the <tt>NOT</tt> Operator
  66. Arithmetic Operators
  67. Summary
  68. Q&amp;A
  69. Workshop
  70. Hour 9. Summarizing Data Results from a Query
  71. What Are Aggregate Functions?
  72. Summary
  73. Q&amp;A
  74. Workshop
  75. Hour 10. Sorting and Grouping Data
  76. Why Group Data?
  77. The <tt>GROUP BY</tt> Clause
  78. <tt>GROUP BY</tt> Versus <tt>ORDER BY</tt>
  79. The <tt>HAVING</tt> Clause
  80. Summary
  81. Q&amp;A
  82. Workshop
  83. Hour 11. Restructuring the Appearance of Data
  84. The Concepts of ANSI Character Functions
  85. Various Common Character Functions
  86. Miscellaneous Character Functions
  87. Mathematical Functions
  88. Conversion Functions
  89. The Concept of Combining Character Functions
  90. Summary
  91. Q&amp;A
  92. Workshop
  93. Hour 12. Understanding Dates and Times
  94. How Is a Date Stored?
  95. Date Functions
  96. Date Conversions
  97. Summary
  98. Q&amp;A
  99. Workshop
  100. Part IV: Building Sophisticated Database Queries
  101. Hour 13. Joining Tables in Queries
  102. Selecting Data from Multiple Tables
  103. Types of Joins
  104. Join Considerations
  105. Summary
  106. Q&amp;A
  107. Workshop
  108. Hour 14. Using Subqueries to Define Unknown Data
  109. What Is a Subquery?
  110. Embedding a Subquery Within a Subquery
  111. Summary
  112. Q&A
  113. Workshop
  114. Hour 15. Combining Multiple Queries into One
  115. Single Queries Versus Compound Queries
  116. Why Would I Ever Want to Use a Compound Query?
  117. Compound Query Operators
  118. Using an <tt>ORDER BY</tt> with a Compound Query
  119. Using <tt>GROUP BY</tt> with a Compound Query
  120. Retrieving Accurate Data
  121. Summary
  122. Workshop
  123. Q&amp;A
  124. Part V: SQL Performance Tuning
  125. Hour 16. Using Indexes to Improve Performance
  126. What Is an Index?
  127. How Do Indexes Work?
  128. The <tt>CREATE INDEX</tt> Command
  129. Types of Indexes
  130. When Should Indexes Be Considered?
  131. When Should Indexes Be Avoided?
  132. Summary
  133. Q&amp;A
  134. Workshop
  135. Hour 17. Improving Database Performance
  136. What Is SQL Statement Tuning?
  137. Database Tuning Versus SQL Tuning
  138. Formatting Your SQL Statement
  139. Full Table Scans
  140. Other Performance Considerations
  141. Performance Tools
  142. Summary
  143. Q&amp;A
  144. Workshop
  145. Part VI: Using SQL to Manage Users and Security
  146. Hour 18. Managing Database Users
  147. Users Are the Reason
  148. The Management Process
  149. Tools Utilized by Database Users
  150. Summary
  151. Q&amp;A
  152. Workshop
  153. Hour 19. Managing Database Security
  154. What Is Database Security?
  155. How Does Security Differ from User Management?
  156. What Are Privileges?
  157. Controlling User Access
  158. Controlling Privileges Through Roles
  159. Summary
  160. Q&amp;A
  161. Workshop
  162. Part VII: Summarized Data Structures
  163. Hour 20. Creating and Using Views and Synonyms
  164. What Is a View?
  165. Creating Views
  166. Dropping a View
  167. What Is a Synonym?
  168. Summary
  169. Q&amp;A
  170. Workshop
  171. Hour 21. Working with the System Catalog
  172. What Is the System Catalog?
  173. How Is the System Catalog Created?
  174. What Is Contained in the System Catalog?
  175. Examples of System Catalog Tables by Implementation
  176. Querying the System Catalog
  177. Updating System Catalog Objects
  178. Summary
  179. Q&amp;A
  180. Workshop
  181. Part VIII: Applying SQL Fundamentals in Today's World
  182. Hour 22. Advanced SQL Topics
  183. Advanced Topics
  184. Cursors
  185. Stored Procedures and Functions
  186. Triggers
  187. Dynamic SQL
  188. Call-Level Interface
  189. Using SQL to Generate SQL
  190. Direct Versus Embedded SQL
  191. Summary
  192. Q&amp;A
  193. Workshop
  194. Hour 23. Extending SQL to the Enterprise, the Internet, and the Intranet
  195. SQL and the Enterprise
  196. Accessing a Remote Database
  197. Accessing a Remote Database Through a Web Interface
  198. SQL and the Internet
  199. SQL and the Intranet
  200. Summary
  201. Q&amp;A
  202. Workshop
  203. Hour 24. Extensions to Standard SQL
  204. Various Implementations
  205. Examples of Extensions from Some Implementations
  206. Interactive SQL Statements
  207. Summary
  208. Q&amp;A
  209. Workshop
  210. Part IX: Appendixes
  211. Appendix A. Common SQL Commands
  212. SQL Statements
  213. SQL Clauses
  214. Appendix B. Using MySQL for Exercises
  215. Windows Installation Instructions
  216. Linux Installation Instructions
  217. Appendix C. Answers to Quizzes and Exercises
  218. Hour 1, "Welcome to the World of SQL"
  219. Hour 2, "Defining Data Structures"
  220. Hour 3, "Managing Database Objects"
  221. Hour 4, "The Normalization Process"
  222. Hour 5, "Manipulating Data"
  223. Hour 6, "Managing Database Transactions"
  224. Hour 7, "Introduction to the Database Query"
  225. Hour 8, "Using Operators to Categorize Data"
  226. Hour 9, "Summarizing Data Results from a Query"
  227. Hour 10, "Sorting and Grouping Data"
  228. Hour 11, "Restructuring the Appearance of Data"
  229. Hour 12, "Understanding Dates and Time"
  230. Hour 13, "Joining Tables in Queries"
  231. Hour 14, "Using Subqueries to Define Unknown Data"
  232. Hour 15, "Combining Multiple Queries into One"
  233. Hour 16, "Using Indexes to Improve Performance"
  234. Hour 17, "Improving Database Performance"
  235. Hour 18, "Managing Database Users"
  236. Hour 19, "Managing Database Security"
  237. Hour 20, "Creating and Using Views and Synonyms"
  238. Hour 21, "Working with the System Catalog"
  239. Hour 22, "Advanced SQL Topics"
  240. Hour 23, "Extending SQL to the Enterprise, the Internet, and the Intranet"
  241. Hour 24, "Extensions to Standard SQL"
  242. Appendix D. <tt>CREATE TABLE</tt> Statements for Book Examples
  243. <tt>EMPLOYEE_TBL</tt>
  244. <tt>EMPLOYEE_PAY_TBL</tt>
  245. <tt>CUSTOMER_TBL</tt>
  246. <tt>ORDERS_TBL</tt>
  247. <tt>PRODUCTS_TBL</tt>
  248. Appendix E. <tt>INSERT</tt> Statements for Data in Book Examples
  249. <tt>INSERT</tt> Statements
  250. Appendix F. Glossary
  251. Appendix G. Bonus Exercises
Recommended Book

Controlling User Access

User access is primarily controlled by a user account and password, but that is not enough to access the database in most major implementations. The creation of a user account is only the first step in allowing access to the database, as well as controlling that access.

After the user account has been created, the database administrator, security officer, or designated individual must be able to assign appropriate system-level privileges to a user for that user to be allowed to perform actual functions within the database, such as creating tables or selecting from tables. Furthermore, the schema owner usually needs to grant database users access to objects in the schema so that the user can do his or her job.

There are two commands in SQL that allow database access control involving the assignment of privileges and the revocation of privileges. The following are the two commands used to distribute both system and object privileges in a relational database:

  • GRANT
  • REVOKE

The GRANT Command

The GRANT command is used to grant both system-level and object-level privileges to an existing database user account.

The syntax is as follows:

   syntax_icon.gif
GRANT PRIVILEGE1 [, PRIVILEGE2 ][ ON OBJECT ]
TO USERNAME [ WITH GRANT OPTION | ADMIN OPTION]

Granting one privilege to a user is as follows:

   input_icon.gif

   GRANT SELECT ON EMPLOYEE_TBL TO USER1;

   output_icon.gif
Grant succeeded.

Granting multiple privileges to a user is as follows:

   input_icon.gif

   GRANT SELECT, INSERT ON EMPLOYEE_TBL TO USER1;

   output_icon.gif
Grant succeeded.

Notice that when granting multiple privileges to a user in a single statement, each privilege is separated by a comma.

Granting privileges to multiple users is as follows:

   input_icon.gif

   GRANT SELECT, INSERT ON EMPLOYEE_TBL TO USER1, USER2;

   output_icon.gif
Grant succeeded.

The syntax to create a user in MySQL is as follows:

   syntax_icon.gif
GRANT USAGE ON DATABASE.TABLES
TO USERNAME@HOST IDENTIFIED BY 'PASSWORD';

GRANT OPTION

GRANT OPTION is a very powerful GRANT command option. When an object's owner grants privileges on an object to another user with GRANT OPTION, the new user can also grant privileges on that object to other users, even though the user does not actually own the object. An example follows:

   input_icon.gif

   GRANT SELECT ON EMPLOYEE_TBL TO USER1 WITH GRANT OPTION;

   output_icon.gif
Grant succeeded.

ADMIN OPTION

ADMIN OPTION is similar to GRANT OPTION in that the user that has been granted the privileges also inherits the ability to grant those privileges to another user. GRANT OPTION is used for object-level privileges, whereas ADMIN OPTION is used for system-level privileges. When a user grants system privileges to another user with ADMIN OPTION, the new user can also grant the system-level privileges to any other user. An example follows:

   mysql_icon.gif
   input_icon.gif

   GRANT CREATE TABLE TO USER1 WITH ADMIN OPTION;

   output_icon.gif
Grant succeeded.

The REVOKE Command

The REVOKE command removes privileges that have been granted to database users. The REVOKE command has two options: RESTRICT and CASCADE. When the RESTRICT option is used, REVOKE succeeds only if the privileges specified explicitly in the REVOKE statement leave no other users with abandoned privileges. The CASCADE option revokes any privileges that would otherwise be left with other users. In other words, if the owner of an object granted USER1 privileges with GRANT OPTION, USER1 granted USER2 privileges with GRANT OPTION, and then the owner revokes USER1's privileges, CASCADE also removes the privileges from USER2.

newterm_icon.gif

Abandoned privileges are privileges that are left with a user who was granted privileges with the GRANT OPTION from a user who has been dropped from the database or had his/her privileges revoked.

The syntax is as follows:

   syntax_icon.gif
REVOKE PRIVILEGE1 [, PRIVILEGE2 ] [ GRANT OPTION FOR ] ON OBJECT
FROM USER { RESTRICT | CASCADE }

The following is an example:

   input_icon.gif

   REVOKE INSERT ON EMPLOYEE_TBL FROM USER1;

   output_icon.gif
Revoke succeeded.

Controlling Access on Individual Columns

Instead of granting object privileges (INSERT, UPDATE, or DELETE) on a table as a whole, you can grant privileges on specific columns in the table to restrict user access, as shown in the following example example:

   input_icon.gif

   GRANT UPDATE (NAME) ON EMPLOYEES TO PUBLIC;

   output_icon.gif
Grant succeeded.

The PUBLIC Database Account

The PUBLIC database user account is a database account that represents all users in the database. All users are part of the PUBLIC account. If a privilege is granted to the PUBLIC account, all database users have the privilege. Likewise, if a privilege is revoked from the PUBLIC account, the privilege is revoked from all database users, unless that privilege was explicitly granted to a specific user. The following is an example:

   input_icon.gif

   GRANT SELECT ON EMPLOYEE_TBL TO PUBLIC;

   output_icon.gif
Grant succeeded.

Groups of Privileges

Some implementations have groups of privileges in the database. These groups of permissions are referred to with different names. Having a group of privileges allows simplicity for granting and revoking common privileges to and from users. For example, if a group consists of ten privileges, the group can be granted to a user instead of all ten privileges.

newterm_icon.gif

SQLBase has groups of privileges called authority levels, whereas these groups of privileges in Oracle are called roles. SQLBase and Oracle both include the following groups of privileges with their implementations:

  • CONNECT
  • RESOURCE
  • DBA

The CONNECT group allows a user to connect to the database and perform operations on any database objects to which the user has access.

The RESOURCE group allows a user to create objects, drop objects he or she owns, grant privileges to objects he or she owns, and so on.

The DBA group allows a user to perform any function within the database. The user can access any database object and perform any operation with this group.

An example for granting a group of privileges to a user follows:

   mysql_icon.gif
   input_icon.gif

   GRANT DBA TO USER1;

   output_icon.gif
Grant succeeded.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.