添加单列
ALTER TABLE tbl_name ADD [COLUMN] col_name column_definition [FIRST|AFTER col_name]
添加多列
（不能指定位置关系）
ALTER TABLE tbl_name ADD [COLUMN] (col_name column_definition,...)
删除列
ALTER TABLE tbl_name DROP [COLUMN] col_name
删除多列
ALTER TABLE tbl_name DROP [COLUMN] col_name，DROP [COLUMN] col_name,...
添加主键约束
ALTER TABLE tbl_name ADD [CONSTRAINT[symbol]] PRIMARY KEY [index_type] (index_col_name,...)
添加唯一约束
ALTER TABLE tbl_name ADD [CONSTRAINT[symbol]] UNIQUE [INDEX|KEY] [index_name] [index_type] (index_col_name,...)
添加外键约束
ALTER TABLE tbl_name ADD [CONSTRAINT[symbol]] FOREIGN KEY [index_name] (index_col_name,...) reference_definition
添加/删除默认约束
ALTER TABLE tbl_name ALTER [COLOUMN] col_name {SET DEFAULT literal|DROP DEFAULT}
删除主键约束
ALTER TABLE tbl_name DROP PRIMARY KEY
删除唯一约束
ALTER TABLE tbl_name DROP {INDEX|KEY} index_name
查看约束名字：SHOW INDEXS FROM tbl_name
删除外键约束
ALTER TABLE tbl_name DROP FROEIGN KEY fk_symbol
查看建表语句：SHOW CREATE TABLE tbl_name
