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https://dev.mysql.com/doc/refman/8.4/en/column-count-limit.html
Functional key parts (see Section 15.1.15, “CREATE INDEX Statement”) are implemented as hidden virtual generated stored columns, so each functional key part in a table index counts against the table total column limit. You have to change some ...
https://dev.mysql.com/doc/refman/8.4/en/problems-with-null.html
For example, the following statements are completely different: mysql> INSERT INTO my_table (phone) VALUES (NULL); mysql> INSERT INTO my_table (phone) VALUES (''); Both statements insert a value into the phone column, but the first inserts a NULL ...
https://dev.mysql.com/doc/workbench/en/wb-performance-explain.html
The visual explain feature generates and displays a visual representation of the MySQL EXPLAIN statement by using extended information available in the extended JSON format. For information about how MySQL executes statements, see Optimizing ...
https://dev.mysql.com/doc/refman/8.4/en/create-table-generated-columns.html
A stored column does require storage space and can be indexed. Other attributes may be given to indicate whether the column is indexed or can be NULL, or provide a comment. If expression evaluation causes truncation or provides incorrect input to a ...Values of a generated column are computed from an expression included in the column ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-ft-deleted-table.html
This value is used when you perform text searches, to skip rows in the INNODB_FT_INDEX_TABLE table before data for deleted rows is physically removed from the FULLTEXT index by an OPTIMIZE TABLE statement. The INNODB_FT_DELETED table stores rows ...
https://dev.mysql.com/doc/refman/8.4/en/symbolic-links-to-tables.html
To determine whether your system supports symbolic links, check the value of the have_symlink system variable using this statement: SHOW VARIABLES LIKE 'have_symlink'; The handling of symbolic links for MyISAM tables works as follows: In the data ...
https://dev.mysql.com/doc/ndbapi/en/ndb-error-codes-internal-error.html
The index needs to be dropped and recreated NDB error code 914 MySQL error DMEC Error message Invalid index stats request NDB error code 916 MySQL error DMEC Error message Invalid index stats sys tables NDB error code 917 MySQL error DMEC Error ...
https://dev.mysql.com/doc/refman/8.4/en/mrr-optimization.html
Reading rows using a range scan on a secondary index can result in many random disk accesses to the base table when the table is large and not stored in the storage engine's cache. With the Disk-Sweep Multi-Range Read (MRR) optimization, MySQL ...
https://dev.mysql.com/doc/refman/8.4/en/myisam-key-cache.html
It employs a cache mechanism to keep the most frequently accessed table blocks in memory: For index blocks, a special structure called the key cache (or key buffer) is maintained. The structure contains a number of block buffers where the most-used ... To minimize disk I/O, the MyISAM storage engine exploits a strategy that is used by many database management ...
https://dev.mysql.com/doc/refman/8.4/en/myisam-table-maintenance.html
This section discusses how to use myisamchk to check or repair MyISAM tables (tables that have .MYD and .MYI files for storing data and indexes). Other table-repair information can be found at Section 3.14, “Rebuilding or Repairing Tables or ...