MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
The date and time data types for representing temporal values are
DATE,
TIME,
DATETIME,
TIMESTAMP, and
YEAR. Each temporal type has a
range of valid values, as well as a “zero” value that
may be used when you specify an invalid value that MySQL cannot
represent. The TIMESTAMP and
DATETIME types have special
automatic updating behavior, described in
Section 11.2.6, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.
For information about storage requirements of the temporal data types, see Section 11.7, “Data Type Storage Requirements”.
For descriptions of functions that operate on temporal values, see Section 12.7, “Date and Time Functions”.
Keep in mind these general considerations 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). For a description of the permitted formats for date and time types, see Section 9.1.3, “Date and Time Literals”. It is expected that you supply valid 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'). To convert strings in other
orders to year-month-day order, the
STR_TO_DATE() function may be
useful.
Dates containing 2-digit year values are ambiguous because the century is unknown. MySQL interprets 2-digit year values using these rules:
Year values in the range 70-99 become
1970-1999.
Year values in the range 00-69 become
2000-2069.
Conversion of values from one temporal type to another occurs according to the rules in Section 11.2.9, “Conversion Between Date and Time Types”.
MySQL automatically converts a date or time value to a number if the value is used in 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 invalid 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.
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 5.1.10, “Server SQL Modes”.) You can get MySQL
to accept certain dates, such as
'2009-11-31', by enabling 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 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 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'. However, with 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
mode.
MySQL permits you to store a “zero” value of
'0000-00-00' as a “dummy
date.” In some cases, this is more convenient than
using NULL values, and uses less data and
index space. To disallow '0000-00-00',
enable the NO_ZERO_DATE
mode.
“Zero” date or time values used through
Connector/ODBC are converted automatically to
NULL because ODBC cannot handle such
values.
The following table shows the format of the “zero”
value for each type. 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. For temporal types that include a date part
(DATE,
DATETIME, and
TIMESTAMP), use of these values may
produce warning or errors. The precise behavior depends on which,
if any, of the strict and
NO_ZERO_DATE SQL modes are
enabled; see Section 5.1.10, “Server SQL Modes”.