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https://dev.mysql.com/doc/refman/8.4/en/delete-optimization.html
The time required to delete individual rows in a MyISAM table is exactly proportional to the number of indexes. To delete all rows from a MyISAM table, TRUNCATE TABLE tbl_name is faster than DELETE FROM tbl_name. Truncate operations are not ...To ...
https://dev.mysql.com/doc/refman/8.4/en/drop-database.html
DROP {DATABASE | SCHEMA} [IF EXISTS] db_name DROP DATABASE drops all tables in the database and deletes the database. Dropping a database does not remove any TEMPORARY tables that were created in that database. TEMPORARY tables are automatically ...
https://dev.mysql.com/doc/refman/8.4/en/encryption-functions.html
One way to make collisions detectable is to make the hash column a primary key. Both HKDF and PBKDF2 can use salts, and their use is recommended to help prevent attacks based on dictionaries of common passwords or rainbow tables. The password is ...
https://dev.mysql.com/doc/refman/8.4/en/estimating-performance.html
For small tables, you can usually find a row in one disk seek (because the index is probably cached). For bigger tables, you can estimate that, using B-tree indexes, you need this many seeks to find a row: log(row_count) / log(index_block_length / 3 ... In most cases, you can estimate query performance by counting disk ...
https://dev.mysql.com/doc/refman/8.4/en/events-metadata.html
To obtain metadata about events: Query the EVENTS table of the INFORMATION_SCHEMA database. Event times can be obtained by selecting from the Information Schema EVENTS table or from SHOW EVENTS, but they are reported as ETZ or STZ values. Value ...
https://dev.mysql.com/doc/refman/8.4/en/faqs-general.html
For the syntax required to perform multiple-table updates, see Section 15.2.17, “UPDATE Statement”; for that required to perform multiple-table deletes, see Section 15.2.2, “DELETE Statement”. A multiple-table insert can be accomplished ...
https://dev.mysql.com/doc/refman/8.4/en/flow-control-functions.html
The default return type of IF() (which may matter when it is stored into a temporary table) is calculated as follows: If expr2 or expr3 produce a string, the result is a string. The second syntax returns the result for the first condition that is ...
https://dev.mysql.com/doc/refman/8.4/en/group-by-functional-dependence.html
The following discussion provides several examples of the ways in which MySQL detects functional dependencies. The examples use this notation: {X} -> {Y} Understand this as “X uniquely determines Y,” which also means that Y is functionally ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-monitoring.html
These Performance Schema tables display information specific to Group Replication: replication_group_member_stats: See Section 20.4.4, “The replication_group_member_stats Table”. These Performance Schema replication tables also show information ... You can use the MySQL Performance Schema to monitor Group ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-online-ddl-failure-conditions.html
A timeout occurs while waiting for an exclusive lock on the table, which may be needed briefly during the initial and final phases of the DDL operation. The operation takes a long time and concurrent DML modifies the table so much that the size of ... The failure of an online DDL operation is typically due to one of the following conditions: An ALGORITHM clause specifies an algorithm that is not compatible with the particular type of DDL operation or storage ...