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https://dev.mysql.com/doc/refman/8.4/en/charset-examples.html
The following examples show how MySQL determines default character set and collation values. Example 2: Table and Column Definition CREATE TABLE t1 ( c1 CHAR(10) CHARACTER SET latin1 ) DEFAULT CHARACTER SET latin1 COLLATE latin1_danish_ci; This ...
https://dev.mysql.com/doc/refman/8.4/en/constant-folding-optimization.html
If the column c were nullable (that is, defined only as TINYINT UNSIGNED) the query would be rewritten like this: SELECT * FROM t WHERE ti IS NOT NULL Folding is performed for constants compared to supported MySQL column types as follows: Integer ...
https://dev.mysql.com/doc/refman/8.4/en/correlated-subqueries.html
So, MySQL looks outside the subquery, and finds t1 in the outer query. In MySQL 8.4.0 and later, operands of the predicate can be column values, constants, or expressions including these, including deterministic functions called with column values ... A correlated subquery is a subquery that contains a reference to a table that also appears in the outer ...
https://dev.mysql.com/doc/refman/8.4/en/corrupted-myisam-tables.html
Even though the MyISAM table format is very reliable (all changes to a table made by an SQL statement are written before the statement returns), you can still get corrupted tables if any of the following events occur: The mysqld process is killed ...An unexpected computer shutdown occurs (for example, the computer is turned ...
https://dev.mysql.com/doc/refman/8.4/en/federated-description.html
To read a result set, it uses mysql_store_result() and fetches rows one at a time using mysql_fetch_row(). A FEDERATED table consists of two elements: A remote server with a database table, which in turn consists of the table definition (stored in ... When you create a table using one of the standard storage engines (such as MyISAM, CSV or InnoDB), the table consists of the table definition and the associated ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-analyze-table-complexity.html
Using these parameters, an approximate formula for estimating ANALYZE TABLE complexity would be: The value of innodb_stats_persistent_sample_pages * number of indexed columns in a table * the number of partitions Typically, the greater the resulting ... ANALYZE TABLE complexity for InnoDB tables is dependent on: The number of pages sampled, as defined by ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-doublewrite-buffer.html
If there is an operating system, storage subsystem, or unexpected mysqld process exit in the middle of a page write, InnoDB can find a good copy of the page from the doublewrite buffer during crash recovery. MySQL supports dynamic changes to the ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-performance-compression-oltp.html
MySQL uses a variable amount of free space for the pages within each compressed table, only when a designated percentage of compression operations “fail” at runtime, requiring an expensive operation to split the compressed page. These ...
https://dev.mysql.com/doc/refman/8.4/en/myisamchk.html
The most effective means of doing so is to shut down the MySQL server while running myisamchk, or to lock all tables that myisamchk is being used on. If mysqld is running, you must force it to flush any table modifications that are still buffered in ... The myisamchk utility gets information about your database tables or checks, repairs, or optimizes ...
https://dev.mysql.com/doc/refman/8.4/en/not-enough-file-handles.html
To tell mysqld to keep open fewer files at a time, you can make the table cache smaller by reducing the value of the table_open_cache system variable (the default value is 64). If you get ERROR 'file_name' not found (errno: 23), Can't open file: ...