MYSQL Build table, add field, modify field SQL statement notation

Build table:

DROP TABLE IF EXISTS Bulletin;

CREATE TABLE Bulletin (
ID INT not NULL PRIMARY key auto_increment, # PRIMARY key
UID INT (one) not NULL DEFAULT 0, # Creator ID
Context VARCHAR (+) not NULL DEFAULT ', # Announcement details (300 words)
BeginTime DEC not NULL DEFAULT 0, # Announcement start time
Endtime DEC not NULL DEFAULT 0, # Announcement end time
Createtime DEC not NULL DEFAULT 0, # creation time
Modifytime DEC (not NULL) DEFAULT 0 # modification Time

PRIMARY KEY (' Id '),
) DEFAULT Charset=utf8 Type=innodb;

Modify the original field name and type:
ALTER TABLE Bulletin Change UID username VARCHAR (+) not NULL DEFAULT ';

To add a new field:

ALTER TABLE Bulletin add citycode varchar (6) NOT null default 0; # City Code

MYSQL Build table, add field, modify field SQL statement notation