Chapter 86. Date and Time Types

Table of Contents

Y2K Issues and Date Types
The DATETIME, DATE, and TIMESTAMP Types
TIMESTAMP behavior when running in MAXDB mode
TIMESTAMP behavior when not running in MAXDB mode
TIMESTAMP properties when running in MAXDB mode
TIMESTAMP properties as of MySQL 4.1 when not running in MAXDB mode
TIMESTAMP properties prior to MySQL 4.1
The TIME Type
The YEAR Type

The date and time types are DATETIME, DATE, TIMESTAMP, TIME, and YEAR. Each of these has a range of legal values, as well as a ``zero'' value that is used when you specify a really illegal value. Note that MySQL allows you to store certain 'not strictly' legal date values, for example 1999-11-31. The reason for this is that we think it's the responsibility of the application to handle date checking, not the SQL servers. To make the date checking 'fast', MySQL only checks that the month is in the range of 0-12 and the day is in the range of 0-31. The above ranges are defined this way because MySQL allows you to store, in a DATE or DATETIME column, dates where the day or month-day is zero. This is extremely useful for applications that need to store a birth-date for which you don't know the exact date. In this case you simply store the date like 1999-00-00 or 1999-01-00. (You cannot expect to get a correct value from functions like DATE_SUB() or DATE_ADD for dates like these.)

Here are some general considerations to keep in mind when working with date and time types:

Y2K Issues and Date Types

MySQL itself is Y2K-safe (see Year 2000 compliance), but input values presented to MySQL may not be. Any input containing 2-digit year values is ambiguous, because the century is unknown. Such values must be interpreted into 4-digit form because MySQL stores years internally using four digits.

For DATETIME, DATE, TIMESTAMP, and YEAR types, MySQL interprets dates with ambiguous year values using the following rules:

  • Year values in the range 00-69 are converted to 2000-2069.

  • Year values in the range 70-99 are converted to 1970-1999.

Remember that these rules provide only reasonable guesses as to what your data mean. If the heuristics used by MySQL don't produce the correct values, you should provide unambiguous input containing 4-digit year values.

ORDER BY will sort 2-digit YEAR/DATE/DATETIME types properly.

Note also that some functions like MIN() and MAX() will convert a TIMESTAMP/DATE to a number. This means that a timestamp with a 2-digit year will not work properly with these functions. The fix in this case is to convert the TIMESTAMP/DATE to 4-digit year format or use something like MIN(DATE_ADD(timestamp,INTERVAL 0 DAYS)).