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https://dev.mysql.com/doc/refman/9.7/en/null-values.html
The NULL value means “no data.” NULL can be written in any lettercase. Be aware that the NULL value is different from values such as 0 for numeric types or the empty string for string types. For text file import or export operations performed ...
https://dev.mysql.com/doc/refman/9.7/en/online-ddl-parallel-thread-configuration.html
The default setting is calculated by the number of available logical processors on the system divided by 8, with a minimum default value of 4. The maximum setting is 256, which is the maximum number for all sessions. The actual number of threads ...
https://dev.mysql.com/doc/refman/9.7/en/optimize-blob.html
For a table with several columns, to reduce memory requirements for queries that do not use the BLOB column, consider splitting the BLOB column into a separate table and referencing it with a join query when needed. When storing a large blob ...
https://dev.mysql.com/doc/refman/9.7/en/optimize-multi-tables.html
When the number of tables runs into the thousands or even millions, the overhead of dealing with all these tables becomes a new performance consideration. Some techniques for keeping individual queries fast involve splitting data across many tables.
https://dev.mysql.com/doc/refman/9.7/en/optimizer-statistics.html
This is needed when reading and parsing histograms from persistent storage into memory. The column_statistics data dictionary table stores histogram statistics about column values, for use by the optimizer in constructing query execution plans. The ...
https://dev.mysql.com/doc/refman/9.7/en/optimizing-innodb-configuration-variables.html
Moving purge operations (a type of garbage collection) into a background thread. Different settings work best for servers with light, predictable loads, versus servers that are running near full capacity all the time, or that experience spikes of ...
https://dev.mysql.com/doc/refman/9.7/en/optimizing-innodb-many-tables.html
This step can take significant time on systems that partition the data into many tables. If you have configured non-persistent optimizer statistics (a non-default configuration), InnoDB computes index cardinality values for a table the first time ...
https://dev.mysql.com/doc/refman/9.7/en/option-modifiers.html
However, you may want to disable it in some instances, such as when sending the output of mysql into another program that expects to see only data and not an initial header line. Some options are “boolean” and control behavior that can be ...
https://dev.mysql.com/doc/refman/9.7/en/option-tracker-component-tables.html
Individual replicas can write their own option usage data into this table. This table, like other Performance Schema tables, is read-only, and thus cannot be updated or truncated by users. See Section 29.12.22.7, “The mysql_option Table”, for ...
https://dev.mysql.com/doc/refman/9.7/en/order-by-optimization.html
Take into account that the size of column values stored in the sort buffer is affected by the max_sort_length system variable value. This section describes when MySQL can use an index to satisfy an ORDER BY clause, the filesort operation used when ...