aaa key

Super key: the attribute set that uniquely identifies a tuples in a link is called the super key of the link mode.Candidate Key: A super key without redundant attributes is called a candidate key.Primary Key (primary key): A candi

one, key and primary key differenceCREATE TABLE Wh_logrecord (logrecord_id Int (one) not NULL auto_increment,User_name varchar (+) default NULL,Operation_time datetime default NULL,Logrecord_operation varchar (+) default NULL,PRIMARY KEY (logrecord_id),KEY Wh_logrecord_user_name (USER_NAME))Analytical:KEY Wh_logrecord_

For example, there are three fields: Table person, person, id (mysql database, primary key, non-auto-increment), and name and pswd. In the case of auto-increment, we usually process insertintoperson (name, pswd) values (# {name}, # {pswd}) in this way. you are not allowed to insert a primary key, because the primary keys of the person table are auto-incrementing. But what if the primary

Key:I understand the public key + private key collectively. Key pair:The Public key (certificate) and private key are in pairs. Each side of the communication holds its own private key and the other's public

When the mysql PRIMARY key is set to auto_increment, the PRIMARY key repeat Duplicate entry 'xxx' for key 'Primary ', duplicateentry occurs during the concurrent performance test. When the mysql PRIMARY key is set to auto_increment, the PRIMARY key repeat Duplicate entry 'xx

First, we need to distinguish the two basic concepts of encryption and authentication.Encryption encrypts data so that illegal users cannot obtain the correct data even if they have obtained the encrypted data. Therefore, data encryption can protect data and prevent attacks. The focus is on data security. Identity Authentication is used to determine the authenticity of an identity. After the identity is confirmed, the system can grant different permissions according to different identities. The

* ** Filename: DropKeyAddKey. SQL * Description: If you want to modify the attribute of the table's primary key field, you need to delete the primary key and then recreate the primary key. The default table is the UserList Test table * Version: 1.0 * Created: 2013.08.2 /* ===================================================== ======================================

Please give us some advice on how to combine the same key values, add the key name values, and then form a new array based on the size of the key name values. Array nbsp; ( nbsp; [615] nbsp ;= gt; nbsp; Ganzhou nbsp; [510] nbsp ;= gt; nbsp; nanchang nbsp; [485] nbsp ;= gt; nbsp; Jiujiang how to combine the same key