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https://dev.mysql.com/doc/refman/5.7/en/dynamic-format.html
NULL columns require additional space in the row to record whether their values are NULL. Each NULL column takes one bit extra, rounded up to the nearest byte. Dynamic storage format is used if a MyISAM table contains any variable-length columns ...
https://dev.mysql.com/doc/refman/5.7/en/events-privileges.html
To enable or disable the execution of scheduled events, it is necessary to set the value of the global event_scheduler system variable. The EVENT privilege governs the creation, modification, and deletion of events. For example, suppose that ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-innodb-metrics-table.html
row *************************** NAME: dml_inserts SUBSYSTEM: dml COUNT: 3 MAX_COUNT: 3 MIN_COUNT: NULL AVG_COUNT: 0.046153846153846156 COUNT_RESET: 3 MAX_COUNT_RESET: 3 MIN_COUNT_RESET: NULL AVG_COUNT_RESET: NULL TIME_ENABLED: 2014-12-04 14:18:28 ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-innodb-sys-virtual-table.html
CREATE TABLE `t1` ( `a` int(11) DEFAULT NULL, `b` int(11) DEFAULT NULL, `c` int(11) GENERATED ALWAYS AS (5) VIRTUAL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4; However, metadata for such a column does appear in the INNODB_SYS_COLUMNS table. The ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-tables-table.html
Not all storage engines update this time, in which case, the value is always NULL. For views, all TABLES columns are NULL except that TABLE_NAME indicates the view name and TABLE_COMMENT says VIEW. The TABLES table has these columns: TABLE_CATALOG ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-fulltext-index.html
If you want to create your own FTS_DOC_ID column, the column must be defined as BIGINT UNSIGNED NOT NULL and named FTS_DOC_ID (all uppercase), as in the following example: Note The FTS_DOC_ID column does not need to be defined as an AUTO_INCREMENT ... Full-text indexes are created on text-based columns (CHAR, VARCHAR, or TEXT columns) to speed up queries and DML operations on data contained within those ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-memcached-internals.html
The mapped key must be a non-Null CHAR or VARCHAR type. There is no length restriction and the value can be NULL. flags: Must be mapped to an INTEGER of at least 32-bits and can be NULL. If there are fewer delimited values than mapped columns, ...
https://dev.mysql.com/doc/refman/5.7/en/json-utility-functions.html
An error results when json_val is not NULL, and is not—or cannot be successfully parsed as—a JSON document. This section documents utility functions that act on JSON values, or strings that can be parsed as JSON values. JSON_PRETTY() prints out ...
https://dev.mysql.com/doc/refman/5.7/en/locking-functions.html
Returns 1 if the lock was obtained successfully, 0 if the attempt timed out (for example, because another client has previously locked the name), or NULL if an error occurred (such as running out of memory or the thread was killed with mysqladmin ...
https://dev.mysql.com/doc/refman/5.7/en/merge-storage-engine.html
The column of the underlying table and the MERGE table can be NULL. The MERGE storage engine, also known as the MRG_MyISAM engine, is a collection of identical MyISAM tables that can be used as one. “Identical” means that all tables have ...