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https://dev.mysql.com/doc/refman/9.7/en/performance-schema-rwlock-instances-table.html
WRITE_LOCKED_BY_THREAD_ID When a thread currently has an rwlock locked in exclusive (write) mode, WRITE_LOCKED_BY_THREAD_ID is the THREAD_ID of the locking thread, otherwise it is NULL. The rwlock_instances table lists all the rwlock (read write ...
https://dev.mysql.com/doc/refman/9.7/en/performance-schema-statement-digests.html
If the table becomes full, the Performance Schema groups statements that have SCHEMA_NAME and DIGEST values not matching existing values in the table in a special row with SCHEMA_NAME and DIGEST set to NULL. The MySQL server is capable of ...
https://dev.mysql.com/doc/refman/9.7/en/performance-schema-summary-tables.html
Generally, the effect is to reset the summary columns to 0 or NULL, not to remove rows. Summary tables provide aggregated information for terminated events over time. The tables in this group summarize event data in different ways. Each summary ...
https://dev.mysql.com/doc/refman/9.7/en/performance-schema-table-characteristics.html
Generally, the effect is to reset the summary columns to 0 or NULL, not to remove rows. The name of the performance_schema database is lowercase, as are the names of tables within it. Many tables in the performance_schema database are read only and ...
https://dev.mysql.com/doc/refman/9.7/en/performance-schema-users-table.html
This is NULL for an internal thread, or for a user session that failed to authenticate. The users table contains a row for each user who has connected to the MySQL server. For each user name, the table counts the current and total number of ...
https://dev.mysql.com/doc/refman/9.7/en/performance-schema-wait-summary-tables.html
This value is calculated only for timed events because nontimed events have a wait time of NULL. The Performance Schema maintains tables for collecting current and recent wait events, and aggregates that information in summary tables. Section ...
https://dev.mysql.com/doc/refman/9.7/en/plugin-loading.html
These can be identified as those that have a library name of NULL in the output from the Information Schema PLUGINS table or SHOW PLUGINS. Server plugins must be loaded into the server before they can be used. It is also possible to control the ...
https://dev.mysql.com/doc/refman/9.7/en/point-in-time-recovery-binlog.html
If your binary log contains \0 (null) characters, that output cannot be parsed by mysql unless you invoke it with the --binary-mode option. This section explains the general idea of using the binary log to perform a point-in-time-recovery. The next ...
https://dev.mysql.com/doc/refman/9.7/en/precision-math.html
Similarly, you can treat division by zero as an error rather than as an operation that produces a result of NULL. MySQL provides support for precision math: numeric value handling that results in extremely accurate results and a high degree control ...
https://dev.mysql.com/doc/refman/9.7/en/query-attribute-components.html
Purpose: Implements the mysql_query_attribute_string() function that takes an attribute name argument and returns the attribute value as a string, or NULL if the attribute does not exist. A component service provides access to query attributes (see ...