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https://dev.mysql.com/doc/refman/8.4/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/8.4/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 ...
https://dev.mysql.com/doc/refman/8.4/en/storage-engines.html
row *************************** Engine: BLACKHOLE Support: YES Comment: /dev/null storage engine (anything you write to it disappears) Transactions: NO XA: NO Savepoints: NO *************************** 5. Blackhole: The Blackhole storage engine ...
https://dev.mysql.com/doc/refman/8.4/en/sys-diagnostics.html
Use NULL to collect data for the default of 60 seconds. Creates a report of the current server status for diagnostic purposes. This procedure disables binary logging during its execution by manipulating the session value of the sql_log_bin system ...
https://dev.mysql.com/doc/refman/8.4/en/sys-processlist.html
db The default database for the thread, or NULL if there is none. current_statement The statement the thread is executing, or NULL if it is not executing any statement. The MySQL process list indicates the operations currently being performed by ...
https://dev.mysql.com/doc/refman/8.4/en/sys-ps-is-consumer-enabled.html
Returns YES or NO to indicate whether a given Performance Schema consumer is enabled, or NULL if the argument is NULL. If the argument is not a valid consumer name, an error occurs. This function accounts for the consumer hierarchy, so a consumer ...
https://dev.mysql.com/doc/refman/8.4/en/sys-ps-is-thread-instrumented.html
Returns YES or NO to indicate whether Performance Schema instrumentation for a given connection ID is enabled, UNKNOWN if the ID is unknown, or NULL if the ID is NULL. This is a value of the type given in the PROCESSLIST_ID column of the ...
https://dev.mysql.com/doc/refman/8.4/en/thread-information.html
row *************************** Id: 5 User: event_scheduler Host: localhost db: NULL Command: Daemon Time: 2756681 State: Waiting on empty queue Info: NULL *************************** 2. To ascertain what your MySQL server is doing, it can be ...
https://dev.mysql.com/doc/refman/8.4/en/user-variables.html
User variables can be assigned a value from a limited set of data types: integer, decimal, floating-point, binary or nonbinary string, or NULL value. If you refer to a variable that has not been initialized, it has a value of NULL and a type of ...
https://dev.mysql.com/doc/refman/8.4/en/using-date.html
When a '0000-00-00' date is used through Connector/ODBC, it is automatically converted to NULL because ODBC cannot handle that kind of date. MySQL permits you to store a “zero” value of '0000-00-00' as a “dummy date.” This is in some cases ...You should use this format in UPDATE expressions and in the WHERE clause of SELECT ...