sql修改数据库中表的结构

ALTER TABLE TableName1
 ADD | ALTER [COLUMN] FieldName1
  FieldType [(nFieldWidth [, nPrecision])]
  [NULL | NOT NULL]
  [CHECK lExpression1 [ERROR cMessageText1]]
  [DEFAULT eExpression1]
  [PRIMARY KEY | UNIQUE]
  [REFERENCES TableName2 [TAG TagName1]]
  [NOCPTRANS] 

例：ALTER TABLE customer ADD COLUMN fax c(20) NULL