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https://dev.mysql.com/doc/refman/8.0/en/mysqlcheck.html
The mysqlcheck client performs table maintenance: It checks, repairs, optimizes, or analyzes tables. Each table is locked and therefore unavailable to other sessions while it is being processed, although for check operations, the table is locked ...
https://dev.mysql.com/doc/refman/8.0/en/myisamchk-table-info.html
To obtain a description of a MyISAM table or statistics about it, use the commands shown here. myisamchk -d tbl_name Runs myisamchk in “describe mode” to produce a description of your table. If you start the MySQL server with external locking ...The output from these commands is explained later in this ...
https://dev.mysql.com/doc/refman/8.0/en/derived-tables.html
The JSON_TABLE() function generates a table and provides another way to create a derived table: SELECT * FROM JSON_TABLE(arg_list) [AS] tbl_name ... For information about lateral derived tables preceded by the LATERAL keyword, see Section 15.2.15.9, ...This does not work: SELECT AVG(SUM(column1)) FROM t1 GROUP BY column1; However, this query provides the desired information: SELECT AVG(sum_column1) FROM (SELECT SUM(column1) AS sum_column1 FROM t1 GROUP BY column1) AS t1; Notice that the column name used within the subquery (sum_column1) is recognized in the outer ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-innodb-tables-table.html
Tables assigned to the system tablespace using CREATE TABLE or ALTER TABLE TABLESPACE=innodb_system have a SPACE_TYPE of General. For related usage information and examples, see Section 17.15.3, “InnoDB INFORMATION_SCHEMA Schema Object Tables”.
https://dev.mysql.com/doc/refman/8.0/en/delete.html
Here is an example of such a scenario: Create a table that contains an indexed AUTO_INCREMENT column. DELETE is a DML statement that removes rows from a table. A DELETE statement can start with a WITH clause to define common table expressions ...To ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-files-table.html
For NDB: The name of an undo log file created by CREATE LOGFILE GROUP or ALTER LOGFILE GROUP, or of a data file created by CREATE TABLESPACE or ALTER TABLESPACE. This means, for example, that the name of a data file created with ALTER TABLESPACE ts ... The FILES table provides information about the files in which MySQL tablespace data is ...For additional information specific to InnoDB, see InnoDB ...
https://dev.mysql.com/doc/refman/8.0/en/merge-table-advantages.html
For example, you can put data from different months into separate tables, compress some of them with myisampack, and then create a MERGE table to use them as one. As a result, MERGE table collections are very fast to create or remap. (You must still ... MERGE tables can help you solve the following problems: Easily manage a set of log ...
https://dev.mysql.com/doc/refman/8.0/en/truncate-table.html
Logically, TRUNCATE TABLE is similar to a DELETE statement that deletes all rows, or a sequence of DROP TABLE and CREATE TABLE statements. It differs from DELETE in the following ways: Truncate operations drop and re-create the table, which is much ...To achieve high performance, TRUNCATE TABLE bypasses the DML method of deleting ...For ...
https://dev.mysql.com/doc/refman/8.0/en/performance-schema-stage-tables.html
The Performance Schema instruments stages, which are steps during the statement-execution process, such as parsing a statement, opening a table, or performing a filesort operation. Stages correspond to the thread states displayed by SHOW ...Within ...
https://dev.mysql.com/doc/refman/8.0/en/performance-schema-summary-tables.html
Summary tables provide aggregated information for terminated events over time. The tables in this group summarize event data in different ways. Each summary table has grouping columns that determine how to group the data to be aggregated, and ...