10.22.1 Problem
You need to make sure a value is equal to or not equal to some specific value, or that it lies within a given range of values.
10.22.2 Solution
Perform a direct comparison.
10.22.3 Discussion
The simplest kind of validation is to perform comparisons against specific literal values:
# require a nonempty value $valid = ($val ne ""); # require a specific nonempty value $valid = ($val eq "abc"); # require one of several values $valid = ($val eq "abc" || $val eq "def" || $val eq "xyz"); # require value in particular range (1 to 10) $valid = ($val >= 1 && $val <= 10);
Most of those tests perform string comparisons. The last is a numeric comparison; however, a numeric comparison often is preceded by preliminary tests to verify first that the value doesn't contain non-numeric characters. Pattern testing, discussed in the next section, is one such way to do that.
String comparisons are case sensitive by default. To make a comparison case insensitive, convert both operands to the same lettercase:
# require a specific nonempty value in case-insensitive fashion $valid = (lc ($val) eq lc ("AbC"));
Using the mysql Client Program
Writing MySQL-Based Programs
Record Selection Techniques
Working with Strings
Working with Dates and Times
Sorting Query Results
Generating Summaries
Modifying Tables with ALTER TABLE
Obtaining and Using Metadata
Importing and Exporting Data
Generating and Using Sequences
Using Multiple Tables
Statistical Techniques
Handling Duplicates
Performing Transactions
Introduction to MySQL on the Web
Incorporating Query Resultsinto Web Pages
Processing Web Input with MySQL
Using MySQL-Based Web Session Management
Appendix A. Obtaining MySQL Software
Appendix B. JSP and Tomcat Primer
Appendix C. References