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MySQL information_schema related content

jacklove

Jun 11, 2018 pm 04:38 PM

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When you install or use MYSQL, you will find that in addition to the database you installed, there is also an information_schema database. What is the information_schema database used for? Friends who use WordPress blogs may wonder, is it necessary to install the database added by the template? After reading this article, you will have an understanding of the information_schema database.

The information_schema database comes with MySQL, which provides a way to access database metadata. What is metadata? Metadata is data about the data, such as database name or table name, column data type, or access permissions, etc. Other terms sometimes used to describe this information include "data dictionary" and "system catalog."

In MySQL, information_schema is regarded as a database, or rather an information database. It holds information about all other databases maintained by the MySQL server. Such as database name, database tables, data types and access rights of table columns, etc. In INFORMATION_SCHEMA, there are several read-only tables. They are actually views, not base tables, so you won't be able to see any files related to them.

information_schema database table description:

SCHEMATA table : Provided in the current mysql instance All database information. The results of show databases are taken from this table.

TABLES table: Provides information about tables in the database (including views). It describes in detail which schema a certain table belongs to, table type, table engine, creation time and other information. The result of show tables from schemaname is taken from this table.

COLUMNS table: provides column information in the table. Detailed description of all columns of a table and information about each column. The result of show columns from schemaname.tablename is taken from this table.

STATISTICS table: Provides information about table indexes. The result of show index from schemaname.tablename is taken from this table.

USER_PRIVILEGES (User Permissions) table: gives information about full permissions. This information is derived from the mysql.user authorization table. Yes and no standard table.

SCHEMA_PRIVILEGES (Scheme Permissions) table: gives information about schema (database) permissions. This information comes from the mysql.db authorization table. Yes and no standard table.

TABLE_PRIVILEGES(Table Permissions) table: gives information about table permissions. This information comes from the mysql.tables_priv grant table. Yes and no standard table.

COLUMN_PRIVILEGES (Column Permissions) table: gives information about column permissions. This information is derived from the mysql.columns_priv grant table. Yes and no standard table.

CHARACTER_SETS (Character Set) table: Provides information about the character sets available for mysql instances. The SHOW CHARACTER SET result set is taken from this table.

COLLATIONS table: provides comparison information about each character set.

COLLATION_CHARACTER_SET_APPLICABILITY table: Specifies the character set that can be used for proofreading. These columns are equivalent to the first two display fields of SHOW COLLATION.

TABLE_CONSTRAINTS table: describes the table where constraints exist. and the constraint type of the table.

KEY_COLUMN_USAGE table: describes the key column with constraints.

ROUTINES table: Provides information about stored subroutines (stored procedures and functions). At this time, the ROUTINES table does not contain custom functions (UDFs). The column named "mysql.proc name" specifies the mysql.proc table column corresponding to the INFORMATION_SCHEMA.ROUTINES table.

VIEWS table: gives information about the views in the database. You need to have show views permission, otherwise you cannot view view information.

TRIGGERS table: Provides information about trigger procedures. You must have super permission to view the table

This article explains the information_schema related content of MySQL. For more related content, please pay attention to the php Chinese website.

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