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https://dev.mysql.com/doc/refman/5.7/en/derived-tables.html
A derived table is an expression that generates a table within the scope of a query FROM clause. For example, a subquery in a SELECT statement FROM clause is a derived table: SELECT ... The [AS] tbl_name clause is mandatory because every table in a ...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/5.7/en/performance-schema-statement-summary-tables.html
The Performance Schema maintains tables for collecting current and recent statement events, and aggregates that information in summary tables. Section 25.12.6, “Performance Schema Statement Event Tables” describes the events on which statement ...Example statement event summary information: mysql> SELECT * FROM performance_schema.events_statements_summary_global_by_event_name\G *************************** ...
https://dev.mysql.com/doc/refman/5.7/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. Thus, it cannot be rolled back, it does not cause ON DELETE triggers to fire, and it cannot be performed for ...To achieve high performance, it bypasses the DML method of deleting ...
https://dev.mysql.com/doc/refman/5.7/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 is the same value that was used in the INITIAL_SIZE clause of the CREATE LOGFILE ... 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/5.7/en/mysql-cluster-online-add-node-example.html
In addition, for each table, the ALTER TABLE statement should be followed by an OPTIMIZE TABLE to reclaim wasted space. However, in NDBCLUSTER tables that existed prior to the addition of the new nodes, neither existing nor new data is distributed ...You can verify that all existing data nodes were restarted using the updated configuration by checking the ndbinfo.nodes table in the mysql ... In this section we provide a detailed example illustrating how to add new NDB Cluster data nodes ...
https://dev.mysql.com/doc/refman/5.7/en/multiple-tables.html
The pet table keeps track of which pets you have. If you want to record other information about them, such as events in their lives like visits to the vet or when litters are born, you need another table. What should this table look like? It needs ...An event type field, if you want to be able to categorize ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-innodb-temp-table-info-table.html
The INNODB_TEMP_TABLE_INFO table provides information about user-created InnoDB temporary tables that are active in an InnoDB instance. It does not provide information about internal InnoDB temporary tables used by the optimizer. The ...The number ...
https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-what-is-new-7-6.html
New features and other important changes in NDB Cluster 7.6 which are likely to be of interest are shown in the following list: New Disk Data table file format. A new file format is used in NDB 7.6 for NDB Disk Data tables, which makes it possible ...You can do this by performing an initial restart of each data node (that is, using the --initial option) as part of the upgrade ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-analyze-table-complexity.html
To set the number of pages sampled for an individual table, use the STATS_SAMPLE_PAGES option with CREATE TABLE or ALTER TABLE. ANALYZE TABLE complexity for InnoDB tables is dependent on: The number of pages sampled, as defined by ...Note ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-event-tables.html
In addition, when events end, the Performance Schema can store them in history tables. For each event type, the Performance Schema uses three tables for storing current and historical events. The tables have names of the following forms, where xxx ... For wait, stage, statement, and transaction events, the Performance Schema can monitor and store current ...