Mysql约束和默认Default---mysql.db

/*Column Information For - mysql.db*/
-------------------------------------

Field                  Type           Collation        Null    Key     Default  Extra   Privileges                       Comment
---------------------  -------------  ---------------  ------  ------  -------  ------  -------------------------------  -------
Host                   char(60)       utf8_bin         NO      PRI                      select,insert,update,references        
Db                     char(64)       utf8_bin         NO      PRI                      select,insert,update,references        
User                   char(16)       utf8_bin         NO      PRI                      select,insert,update,references        
Select_priv            enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Insert_priv            enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Update_priv            enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Delete_priv            enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Create_priv            enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Drop_priv              enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Grant_priv             enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
References_priv        enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Index_priv             enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Alter_priv             enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Create_tmp_table_priv  enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Lock_tables_priv       enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Create_view_priv       enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Show_view_priv         enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Create_routine_priv    enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Alter_routine_priv     enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Execute_priv           enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Event_priv             enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        
Trigger_priv           enum('N','Y')  utf8_general_ci  NO              N                select,insert,update,references        

/*Index Information For - mysql.db*/
------------------------------------

Table   Non_unique  Key_name  Seq_in_index  Column_name  Collation  Cardinality  Sub_part  Packed  Null    Index_type  Comment
------  ----------  --------  ------------  -----------  ---------  -----------  --------  ------  ------  ----------  -------
db               0  PRIMARY              1  Host         A               (NULL)    (NULL)  (NULL)          BTREE             
db               0  PRIMARY              2  Db           A               (NULL)    (NULL)  (NULL)          BTREE             
db               0  PRIMARY              3  User         A                    0    (NULL)  (NULL)          BTREE             
db               1  User                 1  User         A                    0    (NULL)  (NULL)          BTREE             

/*DDL Information For - mysql.db*/
----------------------------------

Table   Create Table                                                                        
------  -------------------------------------------------------------------------------------
db      CREATE TABLE `db` (                                                                 
          `Host` char(60) COLLATE utf8_bin NOT NULL DEFAULT '',                             
          `Db` char(64) COLLATE utf8_bin NOT NULL DEFAULT '',                               
          `User` char(16) COLLATE utf8_bin NOT NULL DEFAULT '',                             
          `Select_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',              
          `Insert_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',              
          `Update_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',              
          `Delete_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',              
          `Create_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',              
          `Drop_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',                
          `Grant_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',               
          `References_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',          
          `Index_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',               
          `Alter_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',               
          `Create_tmp_table_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',    
          `Lock_tables_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',         
          `Create_view_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',         
          `Show_view_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',           
          `Create_routine_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',      
          `Alter_routine_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',       
          `Execute_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',             
          `Event_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',               
          `Trigger_priv` enum('N','Y') CHARACTER SET utf8 NOT NULL DEFAULT 'N',             
          PRIMARY KEY (`Host`,`Db`,`User`),                                                 
          KEY `User` (`User`)                                                               
        ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Database privileges'