13.2.9 日期中的两位数年份
Date values with 2-digit years are ambiguous because the century is unknown. Such values must be interpreted into 4-digit form because MySQL stores years internally using 4 digits.
For DATETIME
, DATE
, and TIMESTAMP
types, MySQL interprets dates specified with ambiguous year values using these rules:
-
Year values in the range
00-69
become2000-2069
. -
Year values in the range
70-99
become1970-1999
.
For YEAR
, the rules are the same, with this exception: A numeric 00
inserted into YEAR
results in 0000
rather than 2000
. To specify zero for YEAR
and have it be interpreted as 2000
, specify it as a string '0'
or '00'
.
Remember that these rules are only heuristics that provide reasonable guesses as to what your data values mean. If the rules used by MySQL do not produce the values you require, you must provide unambiguous input containing 4-digit year values.
ORDER BY
properly sorts YEAR
values that have 2-digit years.
Some functions like MIN()
and MAX()
convert a YEAR
to a number. This means that a value with a 2-digit year does not work properly with these functions. The fix in this case is to convert the YEAR
to 4-digit year format.