10.3. Date and Time Types

The date and time types for representing temporal values are DATETIME, DATE, TIMESTAMP, TIME, and YEAR. Each temporal type has a range of legal values, as well as a “zero” value that may be used when you specify an illegal value that MySQL cannot represent. The TIMESTAMP type has special automatic updating behavior, described later on. For temporal type storage requirements, see Section 10.5, “Data Type Storage Requirements”.

MySQL gives warnings or errors if you try to insert an illegal date. 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 5.1.7, “Server SQL Modes”.) You can get MySQL to accept certain dates, such as '2009-11-31', by using the ALLOW_INVALID_DATES SQL mode. 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 0 to 12 and that the day is in the range from 0 to 31. These ranges are defined to include zero because 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 a birthdate for which you do 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. (If you do not want to permit zero in dates, you can use the NO_ZERO_IN_DATE SQL mode).

A DATE value is coerced to the DATETIME type by adding the time portion as '00:00:00'. To perform the comparison by ignoring the time part of the DATETIME value instead, use the CAST() function to perform the comparison in the following way:

date_col = CAST(NOW() AS DATE)

MySQL also permits you to store '0000-00-00' as a “dummy date” (if you are not using the NO_ZERO_DATE SQL mode). This is in some cases more convenient (and uses less data and index space) than using NULL values.

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

  • 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). Only the formats described in the following sections are supported. It is expected that you supply legal values. Unpredictable results may occur if you use values in other formats.

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

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

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

  • Although MySQL tries to interpret values in several formats, dates always must 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').

  • MySQL automatically converts a date or time type 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 (as described at the beginning of this section), 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.

    The following table shows the format of the “zero” value for each type. Note that the use of these values produces warnings if the NO_ZERO_DATE SQL mode is enabled.

    Data TypeZero” Value
    DATETIME'0000-00-00 00:00:00'
    TIMESTAMP'0000-00-00 00:00:00'
  • The “zero” values are special, but you can store or refer to them explicitly using the values shown in the table. You can also do this using the values '0' or 0, which are easier to write.

  • Zero” date or time values used through MyODBC are converted automatically to NULL in MyODBC 2.50.12 and above, because ODBC cannot handle such values.

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