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https://dev.mysql.com/doc/refman/8.0/en/cost-model.html
Any non-NULL cost estimate specified in the tables takes precedence over the corresponding compiled-in default cost constant. Any NULL estimate indicates to the optimizer to use the compiled-in default. It is also easy to revert to a default by ...
https://dev.mysql.com/doc/refman/8.0/en/create-table-generated-columns.html
Generated column definitions have this syntax: col_name data_type [GENERATED ALWAYS] AS (expr) [VIRTUAL | STORED] [NOT NULL | NULL] [UNIQUE [KEY]] [[PRIMARY] KEY] [COMMENT 'string'] AS (expr) indicates that the column is generated and defines the ...
https://dev.mysql.com/doc/refman/8.0/en/example-auto-increment.html
For example: INSERT INTO animals (id,name) VALUES(0,'groundhog'); If the column is declared NOT NULL, it is also possible to assign NULL to the column to generate sequence numbers. For example: INSERT INTO animals (id,name) VALUES(NULL,'squirrel'); ...You can also explicitly assign 0 to the column to generate sequence numbers, unless the NO_AUTO_VALUE_ON_ZERO SQL mode is ...
https://dev.mysql.com/doc/refman/8.0/en/group-by-functional-dependence.html
A UNIQUE index over a NOT NULL column could be used instead of a primary key and the same functional dependence would apply. As with the previous example, a UNIQUE key over NOT NULL columns could be used instead of a primary key. If in the join ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-innodb-trx-table.html
TRX_REQUESTED_LOCK_ID The ID of the lock the transaction is currently waiting for, if TRX_STATE is LOCK WAIT; otherwise NULL. TRX_WAIT_STARTED The time when the transaction started waiting on the lock, if TRX_STATE is LOCK WAIT; otherwise NULL. The ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-partitions-table.html
SUBPARTITION_NAME If the PARTITIONS table row represents a subpartition, the name of subpartition; otherwise NULL. For partitions whose PARTITION_METHOD is other than RANGE or LIST, this column is always NULL. However, the values of the ...Each row ...
https://dev.mysql.com/doc/refman/8.0/en/invisible-columns.html
Invisible columns support the usual column attributes: NULL, NOT NULL, AUTO_INCREMENT, and so forth. row *************************** Table: t2 Create Table: CREATE TABLE `t2` ( `col1` int DEFAULT NULL, `col2` int DEFAULT NULL ) ENGINE=InnoDB DEFAULT ...An invisible column is normally hidden to queries, but can be accessed if explicitly ...
https://dev.mysql.com/doc/refman/8.0/en/performance-schema-events-transactions-current-table.html
END_EVENT_ID This column is set to NULL when the event starts and updated to the thread current event number when the event ends. If an event is produced from an instrument that has TIMED = NO, timing information is not collected, and TIMER_START, ...The table stores one row per thread showing the current status of the thread's most recent monitored transaction event, so there is no system variable for configuring the table ...
https://dev.mysql.com/doc/refman/8.0/en/replication-gtids-concepts.html
A global transaction identifier (GTID) is a unique identifier created and associated with each transaction committed on the server of origin (the source). This identifier is unique not only to the server on which it originated, but is unique across ...
https://dev.mysql.com/doc/refman/8.0/en/rewriter-query-rewrite-plugin-usage.html
row *************************** id: 1 pattern: SELECT ? pattern_database: NULL replacement: SELECT ? + 1 enabled: YES message: NULL pattern_digest: NULL normalized_pattern: NULL The rule specifies a pattern template indicating which SELECT ... To ...