MySQL retrieves values for a given date or time type in a standard output format, but it attempts to interpret a variety of formats for input values that you supply (for example, when you specify a value to be assigned to or compared to a date or time type). For a description of the permitted formats for date and time types, see Section 8.1.3, “Date and Time Literals”. It is expected that you supply legal values. Unpredictable results may occur if you use values in other formats.

Although MySQL tries to interpret values in several formats, date parts must always be given in year-month-day order (for example, '98-09-04'), rather than in the month-day-year or day-month-year orders commonly used elsewhere (for example, '09-04-98', '04-09-98').

Dates containing two-digit year values are ambiguous because the century is unknown. MySQL interprets two-digit year values using these rules:

See also Section 10.3.6, “Two-Digit Years in Dates”.

Conversion of values from one temporal type to another occurs according to the rules in Section 10.3.5, “Conversion Between Date and Time Types”.

MySQL automatically converts a date or time value to a number if the value is used in a numeric context and vice versa.

By default, when MySQL encounters a value for a date or time type that is out of range or otherwise illegal for the type, it converts the value to the “zero” value for that type. The exception is that out-of-range TIME values are clipped to the appropriate endpoint of the TIME range.

Starting from MySQL 5.0.2, by setting the SQL mode to the appropriate value, you can specify more exactly what kind of dates you want MySQL to support. (See Section 5.1.6, “Server SQL Modes”.) You can get MySQL to accept certain dates, such as '2009-11-31', by enabling the ALLOW_INVALID_DATES SQL mode. (Before 5.0.2, this mode was the default behavior for MySQL.) This is useful when you want to store a “possibly wrong” value which the user has specified (for example, in a web form) in the database for future processing. Under this mode, MySQL verifies only that the month is in the range from 1 to 12 and that the day is in the range from 1 to 31.

MySQL permits you to store dates where the day or month and day are zero in a DATE or DATETIME column. This is extremely useful for applications that need to store birthdates for which you may not know the exact date. In this case, you simply store the date as '2009-00-00' or '2009-01-00'. If you store dates such as these, you should not expect to get correct results for functions such as DATE_SUB() or DATE_ADD() that require complete dates. To disallow zero month or day parts in dates, enable the NO_ZERO_IN_DATE SQL mode.

MySQL permits you to store a “zero” value of '0000-00-00' as a “dummy date.” This is in some cases more convenient than using NULL values, and uses less data and index space. To disallow '0000-00-00', enable the NO_ZERO_DATE SQL mode.

“Zero” date or time values used through Connector/ODBC are converted automatically to NULL because ODBC cannot handle such values.