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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 ...
https://dev.mysql.com/doc/refman/8.0/en/performance-schema-table-wait-summary-tables.html
A value of NULL means that table I/O used no index. The following sections describe the table I/O and lock wait summary tables: table_io_waits_summary_by_index_usage: Table I/O waits per index table_io_waits_summary_by_table: Table I/O waits per ...
https://dev.mysql.com/doc/refman/8.0/en/performance-schema-user-defined-functions-table.html
The value is NULL if the function was registered by a CREATE FUNCTION statement and is in the process of unloading. The value is NULL if the function was registered by a component or plugin rather than by a CREATE FUNCTION statement. The ...
https://dev.mysql.com/doc/refman/8.0/en/prepare.html
A parameter that is an output operand of any of CASE, COALESCE, IF, IFNULL, or NULLIF has the same derived type as the aggregated type of the operator's other output operands. If all output operands of any of CASE, COALESCE, IF, IFNULL, or NULLIF ...
https://dev.mysql.com/doc/refman/8.0/en/primary-key-optimization.html
Query performance benefits from the NOT NULL optimization, because it cannot include any NULL values. The primary key for a table represents the column or set of columns that you use in your most vital queries. With the InnoDB storage engine, the ...
https://dev.mysql.com/doc/refman/8.0/en/processlist-access.html
db is the default database for the thread, or NULL if none has been selected. Info indicates the statement the thread is executing, or NULL if it is executing no statement. The following discussion enumerates the sources of process information, the ...
https://dev.mysql.com/doc/refman/8.0/en/proxy-users.html
Proxy User System Variables Two system variables help trace the proxy login process: proxy_user: This value is NULL if proxying is not used. If the plugin does not set this variable, its value is NULL. The plugin that authenticates a given ...
https://dev.mysql.com/doc/refman/8.0/en/replication-options-binary-log.html
Otherwise, if the table has a unique key all of whose columns are NOT NULL, then only the columns in the unique key need be logged. (If the table has neither a primary key nor a unique key without any NULL columns, then all columns must be used in ... Startup Options Used with Binary Logging System Variables Used with Binary Logging You can use the mysqld options and system variables that are described in this section to affect the operation of the binary log as well as to control which statements are written to the binary ...
https://dev.mysql.com/doc/refman/8.0/en/rewriter-query-rewrite-plugin-reference.html
If no error occurs when the rules table is loaded into memory, the plugin sets the message column to NULL. A non-NULL value indicates an error and the column contents are the error message. Users communicate with the plugin by modifying the set of ...
https://dev.mysql.com/doc/refman/8.0/en/select-into.html
If the FIELDS ESCAPED BY character is empty, no characters are escaped and NULL is output as NULL, not \N. INTO form of SELECT enables a query result to be stored in variables or written to a file: SELECT ... Column and line terminators can be ...