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https://dev.mysql.com/doc/refman/8.4/en/aggregate-functions.html
For MyISAM tables, COUNT(*) is optimized to return very quickly if the SELECT retrieves from one table, no other columns are retrieved, and there is no WHERE clause. COUNT(1) is only subject to the same optimization if the first column is defined as ... This section describes aggregate functions that operate on sets of ...
https://dev.mysql.com/doc/refman/8.4/en/features.html
Support for aliases on tables and columns as required by standard SQL. Each index may consist of 1 to 16 columns or parts of columns. An index may use a prefix of a column for CHAR, VARCHAR, BLOB, or TEXT column types. For example, the Scandinavian ... This section describes some of the important characteristics of the MySQL Database ...
https://dev.mysql.com/doc/refman/8.4/en/index-extensions.html
InnoDB automatically extends each secondary index by appending the primary key columns to it. Consider this table definition: CREATE TABLE t1 ( i1 INT NOT NULL DEFAULT 0, i2 INT NOT NULL DEFAULT 0, d DATE DEFAULT NULL, PRIMARY KEY (i1, i2), INDEX ...This can result in more efficient query execution plans and better ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-buffer-page-table.html
The INNODB_BUFFER_PAGE table has these columns: POOL_ID The buffer pool ID. This column is applicable only to pages with a PAGE_TYPE value of INDEX. The column is NULL if the server has not yet accessed the table. This column is applicable only to ... The INNODB_BUFFER_PAGE table provides information about each page in the InnoDB buffer ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-fields-table.html
The INNODB_FIELDS table provides metadata about the key columns (fields) of InnoDB indexes. The INNODB_FIELDS table has these columns: INDEX_ID An identifier for the index associated with this key field; the same value as INNODB_INDEXES.INDEX_ID.
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-tablestats-table.html
Table statistics are updated only for DELETE or UPDATE operations that modify indexed columns. Statistics are not updated by operations that modify only nonindexed columns. ANALYZE TABLE clears table statistics and sets the STATS_INITIALIZED column ... The INNODB_TABLESTATS table provides a view of low-level status information about InnoDB ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-file-space.html
If a row exceeds the maximum row length, variable-length columns are chosen for external off-page storage until the row fits within the maximum row length limit. External off-page storage for variable-length columns differs by row format: COMPACT ...
https://dev.mysql.com/doc/refman/8.4/en/lateral-derived-tables.html
A derived table cannot normally refer to (depend on) columns of preceding tables in the same FROM clause. Derived tables must be constant over the query's duration, not contain references to columns of other FROM clause tables. A derived table may ...
https://dev.mysql.com/doc/refman/8.4/en/multiple-tables.html
In this example, the ON clause specifies that the name column in the pet table must match the name column in the event table. Because the name column occurs in both tables, you must be specific about which table you mean when referring to the column. This is done by prepending the table name to the column ...
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-limitations-transactions.html
NDBCLUSTER stores only part of a column value that uses any of MySQL's BLOB or TEXT data types in the table visible to MySQL; the remainder of the BLOB or TEXT is stored in a separate internal table that is not accessible to MySQL. This issue does ... A number of limitations exist in NDB Cluster with regard to the handling of ...