A 'ZEROFILL' numeric column will add the UNSIGNED attribute to the column.
UNSIGNED numeric data types also allow SIGNED.
UNSIGNED numeric data types are signed by default.
SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE.
SERIAL DEFAULT VALUE in the definition of an integer column is an alias for NOT NULL AUTO_INCREMENT UNIQUE.
The ZEROFILL can display leading zeros of a number based on the display width.
For example, if you declare an INT(8) ZEROFILL, and the value you're storing is 23, it will be displayed as 00000023.