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
70-99are converted to1970-1999.Year values in the range
00-69are converted to2000-2069.
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
TIMEvalues are clipped to the appropriate endpoint of theTIMErange.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_DATESQL mode is enabled.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'or0, which are easier to write.“Zero” date or time values used through MyODBC are converted automatically to
NULLin MyODBC 2.50.12 and above, because ODBC cannot handle such values.