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https://dev.mysql.com/doc/refman/5.7/en/insert-on-duplicate.html
If column b is also unique, the INSERT is equivalent to this UPDATE statement instead: UPDATE t1 SET c=c+1 WHERE a=1 OR b=2 LIMIT 1; If a=1 OR b=2 matches several rows, only one row is updated. The ON DUPLICATE KEY UPDATE clause can contain multiple ... If you specify an ON DUPLICATE KEY UPDATE clause and a row to be inserted would cause a duplicate value in a UNIQUE index or PRIMARY KEY, an UPDATE of the old row ...
https://dev.mysql.com/doc/refman/5.7/en/myisam-storage-engine.html
Also, the code in the server that fetches column values is not time critical compared to other code. When rows are inserted in sorted order (as when you are using an AUTO_INCREMENT column), the index tree is split so that the high node only contains ... MyISAM is based on the older (and no longer available) ISAM storage engine but has many useful ...
https://dev.mysql.com/doc/refman/5.7/en/myisampack.html
When the table is used later, the server reads into memory the information needed to decompress columns. All tables that are to be combined must have identical structure (same column names and types, same indexes, and so forth). empty-space The ...
https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-disk-data-objects.html
It is also possible to specify whether an individual column is stored on disk or in memory by using a STORAGE clause as part of the column's definition in a CREATE TABLE or ALTER TABLE statement. STORAGE DISK causes the column to be stored on disk, ... NDB Cluster Disk Data storage is implemented using a number of Disk Data ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-key.html
KEY takes only a list of zero or more column names. Any columns used as the partitioning key must comprise part or all of the table's primary key, if the table has one. Where no column name is specified as the partitioning key, the table's primary ... Partitioning by key is similar to partitioning by hash, except that where hash partitioning employs a user-defined expression, the hashing function for key partitioning is supplied by the MySQL ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-memory-summary-tables.html
row *************************** EVENT_NAME: memory/sql/TABLE COUNT_ALLOC: 1381 COUNT_FREE: 924 SUM_NUMBER_OF_BYTES_ALLOC: 2059873 SUM_NUMBER_OF_BYTES_FREE: 1407432 LOW_COUNT_USED: 0 CURRENT_COUNT_USED: 457 HIGH_COUNT_USED: 461 ...Operation counts ...
https://dev.mysql.com/doc/refman/5.7/en/update.html
Multiple-table syntax: UPDATE [LOW_PRIORITY] [IGNORE] table_references SET assignment_list [WHERE where_condition] For the single-table syntax, the UPDATE statement updates columns of existing rows in the named table with new values. The SET clause ... UPDATE is a DML statement that modifies rows in a ...
https://dev.mysql.com/doc/refman/5.7/en/bnl-bka-optimization.html
Suppose that join buffer B1 is employed to join tables t1 and t2 and the result of this operation is joined with table t3 using join buffer B2: A regular join buffer contains columns from each join operand. If B2 is a regular join buffer, each row r ... In MySQL, a Batched Key Access (BKA) Join algorithm is available that uses both index access to the joined table and a join ...
https://dev.mysql.com/doc/refman/5.7/en/engine-condition-pushdown-optimization.html
This optimization improves the efficiency of direct comparisons between a nonindexed column and a constant. (An index access method would be more efficient and so would be chosen in preference to condition pushdown.) Engine condition pushdown ...In ...
https://dev.mysql.com/doc/refman/5.7/en/group-by-optimization.html
The most important preconditions for using indexes for GROUP BY are that all GROUP BY columns reference attributes from the same index, and that the index stores its keys in order (as is true, for example, for a BTREE index, but not for a HASH ...