Validation by Direct Comparison

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

MySQL Cookbook
MySQL Cookbook
ISBN: 059652708X
EAN: 2147483647
Year: 2005
Pages: 412
Authors: Paul DuBois © 2008-2020.
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