UUID and guid
UUID is a string generated after the 32-byte string is separated by four hyphens (-), with a total length of 36 bytes. For example: 550e8400-e29b-41d4-a716-446655440000
Http://gohands.blogbus.com/logs/147479174.html
GUID is Microsoft's implementation of the uuid standard. UUID is defined by the Open Software Foundation (OSF. UUID also has other implementations, more than guid. For example, we use it in Java.
Http://baike.baidu.com/view/1052579.htm
Comb (combine) is a database-specific design concept. It can be understood as an improved guid, which combines the guid and system time, to improve the indexing and retrieval performance.
Http://blog.csdn.net/happyflystone/article/details/1903854
There is no comb type in the database. It was designed by Jimmy Nilsson in his article "The cost of guids as primary keys.
The basic design of the comb data type is as follows: since the uniqueidentifier data causes low indexing efficiency and affects the system performance, can we use a combination, keep the first 10 bytes of uniqueidentifier, and use the last 6 bytes to indicate the time (datetime) generated by the guid. In this way, we combine the time information with uniqueidentifier, while retaining the uniqueness of uniqueidentifier, order is added to Improve Index efficiency.
Http://hi.baidu.com/%CA% AB %D5%B9/blog/item/407fd23f77d5eacf7c1e7122.html
AndroidCode:
Jdk1.5 started to support UUID, Android also supports UUID http://developer.android.com/reference/java/util/UUID.html
UUID generation becomes a simple task, because JDK implements UUID: Java. util. UUID, which can be called directly.
UUID = UUID. randomuuid ();
String S = UUID. randomuuid (). tostring (); // The primary key ID used to generate the database is very good.
ImportJava. util. UUID;
UUID uid = UUID. randomuuid ();
SQLite example
// Insert data
UUID locationid = UUID. randomuuid ();
Contentvalues initialvalues =NewContentvalues ();
Initialvalues. Put ("Rowid", Locationid. tostring ());
//... Other stuff ...//
DB. insert (database_table_locations,Null, Initialvalues );
// Search
Cursor c =
DB. Query (True, Database_table,NewString [] {
"Rowid","Stuff","Things"},"Rowid ='"+ Rowid +"'",
Null,Null,Null,Null);
The above code from: http://groups.google.com/group/android-developers/browse_thread/thread/4a6c40702107fa16
SQL statement
Create Table users
(
Userguid text primary key not null,
Firstname text,
Lastname text
)
Insert into users (userguid, firstname, lastname)
Values ('E7bf9773-8231-44af-8d53-e624f0433943','Bobby','Bobston')
Delete from users where userguid ='E7bf9773-8231-44af-8d53-e624f0433943'
The above statement Source: http://zh-cn.w3support.net/index.php? DB = also & id = 1055848
MySQL
In MySQL, a function generates guid: Select UUID ();
Generally, we use char (36) or binary (36) to store UUID.
Use UUID in PHP
Generate guid in PHP
Http://www.cnblogs.com/ovliverlin/archive/2008/08/27/932444.html
PHP function to generate V4 UUID
Http://stackoverflow.com/questions/2040240/php-function-to-generate-v4-uuid