MySQL Keyword Meaning
NULL The column may contain NULL values. (This setting holds by default.)
NOT NULL The value NULL is not permitted.
DEFAULT xxx The default value xxx will be used if no other value is specified on input.
DEFAULT CURRENT_TIMESTAMP For TIMESTAMP columns, the current time is stored when new records are input.
ON UPDATE CURRENT_TIMESTAMP For TIMESTAMP columns, the current time is stored when changes are made (UPDATE).
PRIMARY KEY Defines the column as a primary key.
AUTO_INCREMENT A sequential number is automatically input.
UNSIGNED Integers are stored without a sign.
CHARACTER SET name [COLLATE sort]For strings, specifies the character set and optionally the desired sort order.