MySQL Cookbook

Using Dates with Missing Components

Problem

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

Solution

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

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')