TAILIEUCHUNG - MySQL Administrator’s Bible- P15

MySQL Administrator’s Bible- P15: Welcome to the MySQL Administrator’s Bible. Like all books in the Bible series, you can expect to find both hands-on tutorials and real-world practical application information, as well as reference and background information that provide a context for what you are learning. | The MySQL Data Dictionary Of yes v - y ti y MySQL stores information about the data in the databases this is called metadata. Much of this information is stored in the INFORMATION_SCHEMA database following the SQL 2003 standard. Tables in the INFORMATION_SCHEMA database are read-only in-memory and show data from various sources. SHOW CREATE TABLE will show the tables as TEMPORARY because they reside in memory and do not persist between mysqld restarts. INFORMATION_SCHEMA tables are called system views and they may be of different storage engine types. At the time of this writing all the system views are either the MEMORY MyISAM or Maria storage engine. Regular SQL statements can be used to query them though they have some special properties that other views do not have mysqldump will not export any information data schema from INFORMATION_SCHEMA system views There is no data directory for the INFORMATION_SCHEMA database There is no .frm file associated with the INFORMATION_SCHEMA views. The definitions are hard-coded into the database. The table definitions for the data dictionary are hard-coded into the source code and loaded when mysqld starts. Unlike other databases there is no directory in the datadir for the INFORMATION_SCHEMA database. All users have permission to see the INFORMATION_SCHEMA database however they can only see the objects they have permission to see. For example table details in the TABLES system view are limited to the tables that the user has permission to see. IN THIS CHAPTER Examining the Object catalog System information Managing permissions Developing custom metadata 667 Part IV Extending Your Skills Some of the metadata provided by the INFORMATION_SCHEMA database is also provided by various SHOW commands see Chapter 4 . The INFORMATION_SCHEMA database is a more complete data dictionary than using SHOW commands. Also standard SQL statements can be used to query the system views to retrieve metadata. The INFORMATION_SCHEMA database .

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