MySQL Cookbook

Performing Validity Checking on Date or Time Subparts

Problem

A string passes a pattern test as a date or time, but you want to perform further checking to make sure that it’s legal.

Solution

Break up the value into subparts and perform the appropriate range checking on each part.

Discussion

Pattern matching may not be sufficient for checking dates or times. For example, a value like 1947-15-19 may match a date pattern, but if you insert the value into a DATE column, MySQL will convert it to 0000-00-00. If you want to find out that the value is bad before putting it into your database, combine pattern matching with range checking.

To make sure that a date is legal, break out the year, month, and day values, then check that they’re within the proper ranges. Years should be less than 9999 (MySQL represents dates to an upper limit of 9999-12-31), month values should be in the range from 1 to 12, and days should be in the range from 1 to the number of days in the month. That latter part is the trickiest; it’s month-dependent, and for February, it’s also year-dependent because it changes for leap years.

Suppose you’re checking input dates in ISO format. Earlier, in Recipe 10.26, we used an is_iso_date( ) function from the Cookbook_Utils.pm library file to perform a pattern match on a date string and break it into component values:

my $ref = is_iso_date ($val); if (defined ($ref)) { # $val matched ISO format pattern; # check its subparts using $ref->[0] through $ref->[2] } else { # $val ...