mysql基础语句
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++mysql 基础操作 
//主键549830479 
   alter table tabelname add new_field_id int(5) unsigned default 0 not null auto_increment ,add primary key (new_field_id); 
//增加一个新列549830479 
   alter table t2 add d timestamp; 
alter table infos add ex tinyint not null default '0'; 
//删除列549830479 
   alter table t2 drop column c; 
//重命名列549830479 
   alter table t1 change a b integer; 
//改变列的类型549830479 
   alter table t1 change b b bigint not null; 
alter table infos change list list tinyint not null default '0'; 
//重命名表549830479 
   alter table t1 rename t2; 
加索引549830479 
   mysql> alter table tablename change depno depno int(5) not null; 
mysql> alter table tablename add index 索引名 (字段名1[，字段名2 …]); 
mysql> alter table tablename add index emp_name (name); 
加主关键字的索引549830479 
mysql> alter table tablename add primary key(id); 
加唯一限制条件的索引549830479 
  mysql> alter table tablename add unique emp_name2(cardnumber); 
删除某个索引549830479 
   mysql>alter table tablename drop index emp_name; 
修改表：549830479 
增加字段：549830479 
   mysql> ALTER TABLE table_name ADD field_name field_type; 
修改原字段名称及类型：549830479 
   mysql> ALTER TABLE table_name CHANGE old_field_name new_field_name field_type; 
删除字段：549830479 
   mysql> ALTER TABLE table_name DROP field_name;  
 
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++mysql 约束 
--------添加主键约束(bookid作为主键)  
alter table bookmessage  
add constraint pk_bookid primary key(bookid)  
--------添加唯一约束  
alter table bookmessage  
add constraint uq_bookid UNIQUE(bookid)  
---------添加默认约束  
alter table bookmessage  
add constraint df_address DEFAUIT('地址不详') for Address  
--------添加检出约束,要求年龄只能在15---40之间  
alter table readermessage  
add constraint CK_age CHECK(age BETWEEN 15 AND 40)  
-------添加外键约束  
alter table bookmessage  
add constraint fk_bookid  
foreign key(bookid)<外键> references readermessage<表>(readerid)<表中的主键>  
-------删除约束  
alter table 表名  
drop constraint 约束名 
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