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https://dev.mysql.com/doc/refman/5.7/en/performance-schema-setup-instruments-table.html
Events produced by the instrument have NULL for the TIMER_START, TIMER_END, and TIMER_WAIT timer values. The setup_instruments table lists classes of instrumented objects for which events can be collected: mysql> SELECT * FROM ...
https://dev.mysql.com/doc/refman/5.7/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/5.7/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/5.7/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/5.7/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/5.7/en/plugin-loading.html
These can be identified as those that have a library name of NULL in the output from INFORMATION_SCHEMA.PLUGINS or SHOW PLUGINS. Server plugins must be loaded into the server before they can be used. It is also possible to control the activation ...
https://dev.mysql.com/doc/refman/5.7/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/5.7/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/5.7/en/rebuilding-tables.html
This section describes how to rebuild or repair tables or indexes, which may be necessitated by: Changes to how MySQL handles data types or character sets. For example, an error in a collation might have been corrected, necessitating a table ...
https://dev.mysql.com/doc/refman/5.7/en/rewriting-subqueries.html
Sometimes there are other ways to test membership in a set of values than by using a subquery. Also, on some occasions, it is not only possible to rewrite a query without a subquery, but it can be more efficient to make use of some of these ...