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https://dev.mysql.com/doc/refman/8.0/en/create-table-secondary-indexes.html
Even with additional write costs, secondary indexes on virtual columns may be preferable to generated stored columns, which are materialized in the clustered index, resulting in larger tables that require more disk space and memory. If a secondary ...A secondary index defined on a virtual column is sometimes referred to as a “virtual ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-online-operations.html
Reads rows from the original table, and writes them to the copy. Other NDB clients can modify row data during a copying ALTER TABLE, resulting in inconsistency. row *************************** Level: Warning Code: 1478 Message: DYNAMIC column c4 ...
https://dev.mysql.com/doc/refman/8.0/en/subquery-optimization-with-exists.html
WHERE subquery_where) MySQL evaluates queries “from outside to inside.” That is, it first obtains the value of the outer expression outer_expr, and then runs the subquery and captures the rows that it produces. A very useful optimization is to ... Certain optimizations are applicable to comparisons that use the IN (or =ANY) operator to test subquery ...
https://dev.mysql.com/doc/refman/8.0/en/comparison-operators.html
The following relational comparison operators can be used to compare not only scalar operands, but row operands: = > < >= <= <> != The descriptions for those operators later in this section detail how they work with row operands. For additional ...
https://dev.mysql.com/doc/refman/8.0/en/grant-tables.html
The server is free to ignore rows that become malformed as a result of such modifications. Each grant table contains scope columns and privilege columns: Scope columns determine the scope of each row in the tables; that is, the context in which the ... The mysql system database includes several grant tables that contain information about user accounts and the privileges held by ...
https://dev.mysql.com/doc/refman/8.0/en/charset-collation-implementations.html
mysql> SET NAMES 'utf8mb4' COLLATE 'utf8mb4_unicode_ci'; Query OK, 0 rows affected (0.05 sec) mysql> SELECT HEX('a'), HEX(WEIGHT_STRING('a')); +----------+-------------------------+ | HEX('a') | HEX(WEIGHT_STRING('a')) | ... MySQL implements several ...
https://dev.mysql.com/doc/refman/8.0/en/example-foreign-keys.html
When an operation affects a key value in the parent table that has matching rows in the child table, the result depends on the referential action specified by ON UPDATE and ON DELETE subclauses of the FOREIGN KEY clause. Omitting ON DELETE and ON ...
https://dev.mysql.com/doc/refman/8.0/en/index-condition-pushdown-optimization.html
Index Condition Pushdown (ICP) is an optimization for the case where MySQL retrieves rows from a table using an index. Without ICP, the storage engine traverses the index to locate rows in the base table and returns them to the MySQL server which ...With ICP enabled, and if parts of the WHERE condition can be evaluated by using only columns from the index, the MySQL server pushes this part of the WHERE condition down to the storage ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-consistent-read.html
This exception causes the following anomaly: If you update some rows in a table, a SELECT sees the latest version of the updated rows, but it might also see older versions of any rows. If another transaction deletes a row and commits after your ...
https://dev.mysql.com/doc/refman/8.0/en/invisible-columns.html
For new or modified rows, violation of a CHECK constraint on an invisible column produces an error. 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 ...