MySQL 4 system Database Introduction

There are some things in MySQL that are similar to SQL Server, while many things are similar to Oracle, and today we share a database management approach that is slightly similar to SQL Server.

1. Information_schema Database: This database provides a way to access database metadata.

Metadata is data about the data, such as database name or table name, the data type of the column, or access permissions. Some of the other terms used to express this information include the data dictionary and the system catalog.
For example:
Mysql> SELECT table_name, TABLE_TYPE, engine from Information_schema.tables
-WHERE Table_schema = ' HR '
ORDER by table_name DESC;
It holds information about all other databases maintained by the MySQL server and the master database type in SQL Server. There are several read-only tables in the INFORMATION_SCHEMA. In fact, they are views, not basic tables, so you won't be able to see any files associated with them. Each MySQL user has access to these tables, but only to specific rows in the table, where the user has the appropriate access rights to the object.
The only way to access the tables contained in the database information_schema is to use the SELECT statement. Because the contents of the metadata can not be arbitrarily insert, update and Delete, and so on.
It reflects information about MySQL database data, if you can modify it will cause the database is not normal use. If you want to modify the description information about the table and the field, it is not directly in the INFORMATION_SCHEMA modification, but need to modify the corresponding table in the database, after modifying a database object, INFORMATION_SCHEMA data will be automatically updated.

2. Performance_schema Database: This database provides important reference information for database performance optimization, which is turned off by default and needs to be turned on in My.ini or MY.CNF (Linux system), which is a static setting. The dynamic setting does not take effect immediately at run time. These include some current event information, historical event information, and aggregated statistics. The database combined with slow query, and explain statements can be generalized
Performance optimizations and statement improvements.

3. mysql database: This database is also a core database, storing user's permission information and help information. It is not possible to modify its contents.

4.TEST database: This is the MySQL after the later version of the database, this database is not reused, after the installation of MySQL system automatically established this database, by default, the inside is empty, there is no database object for users to test the use, the user can also delete it, There is no impact on the system.

Remark:it essay, if reproduced please indicate out, thank you!

Terryxia

MySQL 4 system Database Introduction