Comparison of Mysql, Oracle, DB2

Process- -- database - Object

Process -Server -User - Object

Process -database -User - Schema - Object

MySQL, Oracle, Db2

Have not done Oracle multi-instance, DB2 is also just touching, plain understanding

MySQL this way is very early most people think, database and user is separated from the other two, with authorization to associate users and databases.

In the JDBC connection address, the three specify the database, user, User (&schema), Db2 If you do not create a Schema alone, the form is the same as Oracle. DB2 user can only be operating system users, the database itself can not create users, this seems not very good, for different applications, MySQL is to create a different database,oracle is to create a different user, then Db2 there are two ways to create a different operating system users , the second is to create a different schema under user, and then the JDBC Connection address declares the schema.

On the application division level, the database, User and schema of three kinds of databases are at one level. Oracle can create multiple instances compared to MySQL, and one instance is equivalent to a MySQL process, and my understanding of Oracle's creation is to create a database that creates a new oracleserver. DB2 database and Oracle instance at one level, the difference is that Oracle creates an instance is more troublesome, Db2 a sentence to execute. Two instances of Oracle are independent, DB2 is also. Access needs to be done in a specific way.

Unified speaking,

1:oracle instance and DB2 database is one thing, should be unified known as the case is more appropriate, and MySQL is a single-instance mode

2: Application division layer, the three are database, user, schema, unified called database is more appropriate, the real data are in this layer.

It is understood from here that the function of username and password is only used to log in and give access to database.

The two are irrelevant in MySQL.

Oracle here does not have the concept of database, user is the database, it can be understood to create a user while creating a database with the same name. Several user have several database.

DB2 Creating a user creates a database as the schema with the same name, and another schema can be created.