Using Dates with Missing Components

10.33.1 Problem

The dates in your data are incomplete, that is, they have missing subparts.

10.33.2 Solution

MySQL can represent them as ISO dates using zero for the missing parts.

10.33.3 Discussion

Some applications use dates that are not complete. For example, you may need to work with input values such as Mar/2001 that contain only a month and year. As of MySQL 3.23, it's possible to represent such values as ISO-format dates that have zero in the "missing" parts. (The value Mar/2001 can be stored as 2001-03-00.) To convert month/year values to ISO format for import into MySQL, set up a hash to map month names to their numeric values:

my %map = # map 3-char month abbreviations to numeric month
(
 "jan" => 1, "feb" => 2, "mar" => 3, "apr" => 4, "may" => 5, "jun" => 6,
 "jul" => 7, "aug" => 8, "sep" => 9, "oct" => 10, "nov" => 11, "dec" => 12
);

Then convert each input value like this:

if ($val =~ /^([a-z]{3})/(d{4})$/i)
{
 my ($m, $y) = (lc ($1), $2); # use lowercase month name
 $val = sprintf ("%04d-%02d-00", $y, $map{$m})
}

After storing the resulting values into MySQL, you can retrieve them for display in the original month/year format by issuing a SELECT statement that rewrites the dates using a DATE_FORMAT( ) expression:

DATE_FORMAT(date_val,'%b/%Y')

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

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