Server SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients.
depending on the value of the sql_mode systemn varable.
DBAs can set the global SQL mode to match site server operating requirements, and each application can set its session SQL mode to its own requirements.

ALLOW_INVALID_DATES
Do no tpreform full checking o dates. check only that the month is in the range from 1 to 12 and the day in the range from 1 to 31.
THis may be useful for Web application that obntain year,mouth ,and day in three different fields and store exactly what the user inserted , without date validation.
This mode applies to DATE and DATETIME clolumns.
It does not apply TIMESTAMP clolumns, which always require a valid date.
if ALLOW_INVALID_DATES disabled. '2004-4-31' 这种不合理的日期会被转换为'0000-00-00'并且会报错...