- MySQL Cookbook
- A Note Regarding Supplemental Files
- Preface
- 1. Using the mysql Client Program
- Introduction
- Setting Up a MySQL User Account
- Creating a Database and a Sample Table
- Starting and Stopping mysql
- Specifying Connection Parameters Using Option Files
- Protecting Option Files from Other Users
- Mixing Command-Line and Option File Parameters
- What to Do if mysql Cannot Be Found
- Issuing SQL Statements
- Canceling a Partially Entered Statement
- Repeating and Editing SQL Statements
- Using Auto-Completion for Database and Table Names
- Telling mysql to Read Statements from a File
- Telling mysql to Read Statements from Other Programs
- Entering an SQL One-Liner
- Using Copy and Paste as a mysql Input Source
- Preventing Query Output from Scrolling off the Screen
- Sending Query Output to a File or to a Program
- Selecting Tabular or Tab-Delimited Query Output Format
- Specifying Arbitrary Output Column Delimiters
- Producing HTML or XML Output
- Suppressing Column Headings in Query Output
- Making Long Output Lines More Readable
- Controlling mysql’s Verbosity Level
- Logging Interactive mysql Sessions
- Creating mysql Scripts from Previously Executed Statements
- Using User-Defined Variables in SQL Statements
- Numbering Query Output Lines
- Using mysql as a Calculator
- Using mysql in Shell Scripts
- 2. Writing MySQL-Based Programs
- Introduction
- Connecting, Selecting a Database, and Disconnecting
- Checking for Errors
- Writing Library Files
- Issuing Statements and Retrieving Results
- Handling Special Characters and NULL Values in Statements
- Handling Special Characters in Identifiers
- Identifying NULL Values in Result Sets
- Techniques for Obtaining Connection Parameters
- Conclusion and Words of Advice
- 3. Selecting Data from Tables
- Introduction
- Specifying Which Columns to Select
- Specifying Which Rows to Select
- Giving Better Names to Query Result Columns
- Using Column Aliases to Make Programs Easier to Write
- Combining Columns to Construct Composite Values
- WHERE Clauses and Column Aliases
- Debugging Comparison Expressions
- Removing Duplicate Rows
- Working with NULL Values
- Writing Comparisons Involving NULL in Programs
- Sorting a Result Set
- Using Views to Simplify Table Access
- Selecting Data from More Than One Table
- Selecting Rows from the Beginning or End of a Result Set
- Selecting Rows from the Middle of a Result Set
- Choosing Appropriate LIMIT Values
- What to Do When LIMIT Requires the Wrong Sort Order
- Calculating LIMIT Values from Expressions
- 4. Table Management
- 5. Working with Strings
- Introduction
- String Properties
- Choosing a String Data Type
- Setting the Client Connection Character Set Properly
- Writing String Literals
- Checking a String’s Character Set or Collation
- Changing a String’s Character Set or Collation
- Converting the Lettercase of a String
- Converting the Lettercase of a Stubborn String
- Controlling Case Sensitivity in String Comparisons
- Pattern Matching with SQL Patterns
- Pattern Matching with Regular Expressions
- Controlling Case Sensitivity in Pattern Matching
- Breaking Apart or Combining Strings
- Searching for Substrings
- Using FULLTEXT Searches
- Using a FULLTEXT Search with Short Words
- Requiring or Excluding FULLTEXT Search Words
- Performing Phrase Searches with a FULLTEXT Index
- 6. Working with Dates and Times
- Introduction
- Choosing a Temporal Data Type
- Changing MySQL’s Date Format
- Setting the Client Time Zone
- Determining the Current Date or Time
- Using TIMESTAMP to Track Row Modification Times
- Extracting Parts of Dates or Times
- Synthesizing Dates or Times from Component Values
- Converting Between Temporal Data Types and Basic Units
- Calculating the Interval Between Two Dates or Times
- Adding Date or Time Values
- Calculating Ages
- Shifting a Date-and-Time Value to a Different Time Zone
- Finding the First Day, Last Day, or Length of a Month
- Calculating Dates by Substring Replacement
- Finding the Day of the Week for a Date
- Finding Dates for Any Weekday of a Given Week
- Performing Leap Year Calculations
- Canonizing Not-Quite-ISO Date Strings
- Treating Dates or Times as Numbers
- Forcing MySQL to Treat Strings as Temporal Values
- Selecting Rows Based on Their Temporal Characteristics
- 7. Sorting Query Results
- Date-Based Sorting
- Sorting by Calendar Day
- Sorting by Day of Week
- Sorting by Time of Day
- Sorting Using Substrings of Column Values
- Sorting by Fixed-Length Substrings
- Sorting by Variable-Length Substrings
- Sorting Hostnames in Domain Order
- Sorting Dotted-Quad IP Values in Numeric Order
- Floating Values to the Head or Tail of the Sort Order
- Sorting in User-Defined Orders
- Sorting ENUM Values
- 8. Generating Summaries
- Introduction
- Summarizing with COUNT()
- Summarizing with MIN() and MAX()
- Summarizing with SUM() and AVG()
- Using DISTINCT to Eliminate Duplicates
- Finding Values Associated with Minimum and Maximum Values
- Controlling String Case Sensitivity for MIN() and MAX()
- Dividing a Summary into Subgroups
- Summaries and NULL Values
- Selecting Only Groups with Certain Characteristics
- Using Counts to Determine Whether Values Are Unique
- Grouping by Expression Results
- Categorizing Noncategorical Data
- Controlling Summary Display Order
- Finding Smallest or Largest Summary Values
- Date-Based Summaries
- Working with Per-Group and Overall Summary Values Simultaneously
- Generating a Report That Includes a Summary and a List
- 9. Obtaining and Using Metadata
- Introduction
- Obtaining the Number of Rows Affected by a Statement
- Obtaining Result Set Metadata
- Determining Whether a Statement Produced a Result Set
- Using Metadata to Format Query Output
- Listing or Checking Existence of Databases or Tables
- Accessing Table Column Definitions
- Getting ENUM and SET Column Information
- Using Table Structure Information in Applications
- Getting Server Metadata
- Writing Applications That Adapt to the MySQL Server Version
- Determining the Default Database
- Monitoring the MySQL Server
- Determining Which Storage Engines the Server Supports
- 10. Importing and Exporting Data
- Introduction
- Importing Data with LOAD DATA and mysqlimport
- Specifying the Datafile Location
- Specifying the Structure of the Datafile
- Dealing with Quotes and Special Characters
- Importing CSV Files
- Reading Files from Different Operating Systems
- Handling Duplicate Key Values
- Obtaining Diagnostics About Bad Input Data
- Skipping Datafile Lines
- Specifying Input Column Order
- Preprocessing Input Values Before Inserting Them
- Ignoring Datafile Columns
- Exporting Query Results from MySQL
- Exporting Tables as Text Files
- Exporting Table Contents or Definitions in SQL Format
- Copying Tables or Databases to Another Server
- Writing Your Own Export Programs
- Converting Datafiles from One Format to Another
- Extracting and Rearranging Datafile Columns
- Using the SQL Mode to Control Bad Input Data Handling
- Validating and Transforming Data
- Using Pattern Matching to Validate Data
- Using Patterns to Match Broad Content Types
- Using Patterns to Match Numeric Values
- Using Patterns to Match Dates or Times
- Using Patterns to Match Email Addresses or URLs
- Using Table Metadata to Validate Data
- Using a Lookup Table to Validate Data
- Converting Two-Digit Year Values to Four-Digit Form
- Performing Validity Checking on Date or Time Subparts
- Writing Date-Processing Utilities
- Using Dates with Missing Components
- Importing Non-ISO Date Values
- Exporting Dates Using Non-ISO Formats
- Importing and Exporting NULL Values
- Guessing Table Structure from a Datafile
- Exchanging Data Between MySQL and Microsoft Access
- Exchanging Data Between MySQL and Microsoft Excel
- Exporting Query Results as XML
- Importing XML into MySQL
- Epilogue
- 11. Generating and Using Sequences
- Introduction
- Creating a Sequence Column and Generating Sequence Values
- Choosing the Data Type for a Sequence Column
- The Effect of Row Deletions on Sequence Generation
- Retrieving Sequence Values
- Renumbering an Existing Sequence
- Extending the Range of a Sequence Column
- Reusing Values at the Top of a Sequence
- Ensuring That Rows Are Renumbered in a Particular Order
- Starting a Sequence at a Particular Value
- Sequencing an Unsequenced Table
- Using an AUTO_INCREMENT Column to Create Multiple Sequences
- Managing Multiple Simultaneous AUTO_INCREMENT Values
- Using AUTO_INCREMENT Values to Relate Tables
- Using Sequence Generators as Counters
- Generating Repeating Sequences
- Numbering Query Output Rows Sequentially
- 12. Using Multiple Tables
- Introduction
- Finding Rows in One Table That Match Rows in Another
- Finding Rows with No Match in Another Table
- Comparing a Table to Itself
- Producing Master-Detail Lists and Summaries
- Enumerating a Many-to-Many Relationship
- Finding Rows Containing Per-Group Minimum or Maximum Values
- Computing Team Standings
- Using a Join to Fill or Identify Holes in a List
- Calculating Successive-Row Differences
- Finding Cumulative Sums and Running Averages
- Using a Join to Control Query Output Order
- Combining Several Result Sets in a Single Query
- Identifying and Removing Mismatched or Unattached Rows
- Performing a Join Between Tables in Different Databases
- Using Different MySQL Servers Simultaneously
- Referring to Join Output Column Names in Programs
- 13. Statistical Techniques
- Introduction
- Calculating Descriptive Statistics
- Per-Group Descriptive Statistics
- Generating Frequency Distributions
- Counting Missing Values
- Calculating Linear Regressions or Correlation Coefficients
- Generating Random Numbers
- Randomizing a Set of Rows
- Selecting Random Items from a Set of Rows
- Assigning Ranks
- 14. Handling Duplicates
- 15. Performing Transactions
- Introduction
- Choosing a Transactional Storage Engine
- Performing Transactions Using SQL
- Performing Transactions from Within Programs
- Using Transactions in Perl Programs
- Using Transactions in Ruby Programs
- Using Transactions in PHP Programs
- Using Transactions in Python Programs
- Using Transactions in Java Programs
- Using Alternatives to Transactions
- 16. Using Stored Routines, Triggers, and Events
- Introduction
- Creating Compound-Statement Objects
- Using a Stored Function to Encapsulate a Calculation
- Using a Stored Procedure to Return Multiple Values
- Using a Trigger to Define Dynamic Default Column Values
- Simulating TIMESTAMP Properties for Other Date and Time Types
- Using a Trigger to Log Changes to a Table
- Using Events to Schedule Database Actions
- 17. Introduction to MySQL on the Web
- 18. Incorporating Query Results into Web Pages
- Introduction
- Displaying Query Results as Paragraph Text
- Displaying Query Results as Lists
- Displaying Query Results as Tables
- Displaying Query Results as Hyperlinks
- Creating a Navigation Index from Database Content
- Storing Images or Other Binary Data
- Retrieving Images or Other Binary Data
- Serving Banner Ads
- Serving Query Results for Download
- Using a Template System to Generate Web Pages
- 19. Processing Web Input with MySQL
- Introduction
- Writing Scripts That Generate Web Forms
- Creating Single-Pick Form Elements from Database Content
- Creating Multiple-Pick Form Elements from Database Content
- Loading a Database Record into a Form
- Collecting Web Input
- Validating Web Input
- Storing Web Input in a Database
- Processing File Uploads
- Performing Searches and Presenting the Results
- Generating Previous-Page and Next-Page Links
- Generating Click to Sort Table Headings
- Web Page Access Counting
- Web Page Access Logging
- Using MySQL for Apache Logging
- Introduction
- Using MySQL-Based Sessions in Perl Applications
- Using MySQL-Based Storage in Ruby Applications
- Using MySQL-Based Storage with the PHP Session Manager
- Using MySQL for Session-Backing Store with Tomcat
- A. Obtaining MySQL Software
- B. Executing Programs from the Command Line
- C. JSP and Tomcat Primer
- D. References
- Index
- About the Author
- Colophon
- Copyright
SELECTDATABASE() returns the name of the
default database or NULL if no
database has been selected. The following Ruby code uses the statement
to present a status display containing information about the current
connection:
db = dbh.select_one("SELECT DATABASE()")[0]
puts "Default database: " + (db.nil? ? "(no database selected)" : db)Note that before MySQL 4.1.1, DATABASE() returns an empty string
(not NULL) if there is no current
database.
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