Detailed explanation of the role of the default database after MySQL installation

When you learn MySQL, you will find that it comes with several default databases after installation. The MySQL 5.5 I installed comes with six databases.

I checked some information online to learn about the functions of these databases.

1. information_schema

There are many tables in this library.

Information_schema database table description:

SCHEMATA table: provides information about all databases in the current MySQL instance. 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 the schema to which a table belongs, the table type, table engine, creation time and other information. The result of show tables from schemaname is taken from this table.

COLUMNS table: provides information about the columns in the table. It describes in detail all the columns of a table and the information of 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 global permissions. This information comes from the mysql.user grant table. This is a non-standard table.

SCHEMA_PRIVILEGES (schema privileges) table: gives information about schema (database) privileges. This information comes from the mysql.db grant table. This is a non-standard table.

TABLE_PRIVILEGES (table privileges) table: gives information about table privileges. This information is derived from the mysql.tables_priv grant table. This is a non-standard table.

COLUMN_PRIVILEGES (column privileges) table: gives information about column privileges. This information is derived from the mysql.columns_priv grant table. This is a non-standard table.

CHARACTER_SETS (character set) table: provides information about the character sets available for the MySQL instance. The result set of SHOW CHARACTER SET is taken from this table.

COLLATIONS table: Provides comparison information about each character set.

COLLATION_CHARACTER_SET_APPLICABILITY table: specifies the character sets that can be used for collation. These columns are equivalent to the first two display fields of SHOW COLLATION.

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

KEY_COLUMN_USAGE table: describes the key columns with constraints.

ROUTINES table: Provides information about stored routines (stored procedures and functions). At this time, the ROUTINES table does not contain user-defined functions (UDFs). The column named "mysql.proc name" identifies the mysql.proc table column that corresponds to the INFORMATION_SCHEMA.ROUTINES table.

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

TRIGGERS table: Provides information about triggers. You must have super privileges to view this table.

2.mysql

3.performance_schema

You need to set the parameter: performance_schema to enable this function

The event statistics table is based on the relevant standards. The table is also read-only and can only be turcate

events_waits_summary_by_instance

events_waits_summary_by_thread_by_event_name

events_waits_summary_global_by_event_name

file_summary_by_event_name

file_summary_by_instance

setup_consumers describes various events

setup_instruments describes the table name under this database and whether monitoring is enabled.

setup_timers describes monitoring options and sampling frequency intervals

events_waits_current records the currently occurring wait events. This table is read-only and cannot be updated or deleted, but can be truncated.

Performance history table: events_waits_history only retains the most recent 10 events for each thread

Performance history table: events_waits_history_long records the last 10,000 events in a standard first-in-first-out (FIFO) format. These two tables are also read-only tables and can only be truncated.

4.sakila

This is a sample MySQL database with some example tables.

5.test

This is an empty table, a test table, and can be deleted.

6.world

This table is not very useful, as there is a lot of data in these three tables. I will continue to add more as I make progress. .

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