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https://dev.mysql.com/doc/refman/8.0/en/merge-storage-engine.html
The MERGE storage engine, also known as the MRG_MyISAM engine, is a collection of identical MyISAM tables that can be used as one. You cannot merge MyISAM tables in which the columns are listed in a different order, do not have exactly the same ...
https://dev.mysql.com/doc/refman/8.0/en/merge-table-problems.html
The following are known problems with MERGE tables: MERGE child tables are locked through the parent table. If you use ALTER TABLE to change a MERGE table to another storage engine, the mapping to the underlying tables is lost. The INSERT_METHOD ...
https://dev.mysql.com/doc/refman/8.0/en/index-merge-optimization.html
The Index Merge access method retrieves rows with multiple range scans and merges their results into one. This access method merges index scans from a single table only, not scans across multiple tables. The merge can produce unions, intersections, ...In this case, the key column contains a list of indexes used, and key_len contains a list of the longest key parts for those ...
https://dev.mysql.com/doc/refman/8.0/en/merge-table-advantages.html
MERGE tables can help you solve the following problems: Easily manage a set of log tables. For example, you can put data from different months into separate tables, compress some of them with myisampack, and then create a MERGE table to use them as ...You can split a large read-only table based on some criteria, and then put individual tables on different ...
https://dev.mysql.com/doc/refman/8.0/en/index-page-merge-threshold.html
If the “page-full” percentage for an index page falls below the MERGE_THRESHOLD value when a row is deleted or when a row is shortened by an UPDATE operation, InnoDB attempts to merge the index page with a neighboring index page. The default ...
https://dev.mysql.com/doc/refman/8.0/en/derived-table-optimization.html
(For an example, see Section 10.2.2.2, “Optimizing Subqueries with Materialization”.) If merging would result in an outer query block that references more than 61 base tables, the optimizer chooses materialization instead. The following means ...
https://dev.mysql.com/doc/refman/8.0/en/optimizer-hints.html
If subqueries subq1 and subq2 are converted to semijoins, tables t4@subq1 and t5@subq2 are merged to the outer query block. Whether derived tables, view references, or common table expressions should be merged into the outer query block, or ... One ...
https://dev.mysql.com/doc/refman/8.0/en/json-modification-functions.html
Synonym for JSON_MERGE_PRESERVE(); deprecated in MySQL 8.0.3 and subject to removal in a future release. mysql> SELECT JSON_MERGE('[1, 2]', '[true, false]'); +---------------------------------------+ | JSON_MERGE('[1, 2]', '[true, false]') | ... The ...
https://dev.mysql.com/doc/refman/8.0/en/view-algorithms.html
For MERGE, the text of a statement that refers to the view and the view definition are merged such that parts of the view definition replace corresponding parts of the statement. It prefers MERGE over TEMPTABLE if possible, because MERGE is usually ... The optional ALGORITHM clause for CREATE VIEW or ALTER VIEW is a MySQL extension to standard ...
https://dev.mysql.com/doc/refman/8.0/en/switchable-optimizations.html
For more information, see Section 10.2.2.5, “Derived Condition Pushdown Optimization” Derived Table Merging Flags derived_merge (default on) Controls merging of derived tables and views into outer query block. The derived_merge flag controls ...