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https://dev.mysql.com/doc/refman/5.7/en/information-schema-introduction.html
INFORMATION_SCHEMA provides access to database metadata, information about the MySQL server such as the name of a database or table, the data type of a column, or access privileges. Character Set Considerations The definition for character columns ...Other terms that are sometimes used for this information are data dictionary and system ...
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/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/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/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 ...
https://dev.mysql.com/doc/refman/5.7/en/identifier-qualifiers.html
ON mydb.mytable ...; A column name may be given multiple qualifiers to indicate context in statements that reference it, as shown in the following table. Suppose that column c1 occurs only in table t1, c2 only in t2, and c in both t1 and t2. Suppose ...An unqualified name is permitted in contexts where interpretation of the name is ...
https://dev.mysql.com/doc/refman/5.7/en/known-issues.html
DISTINCT with ORDER BY does not work inside GROUP_CONCAT() if you do not use all and only those columns that are in the DISTINCT list. When inserting a big integer value (between 263 and 264−1) into a decimal or string column, it is inserted as a ... This section lists known issues in recent versions of ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-hash.html
This can simply be the name of a column whose type is one of MySQL's integer types. You should be aware that, if a table has any unique keys, every column used in the partitioning expression for this table must be part of every unique key, including ... Partitioning by HASH is used primarily to ensure an even distribution of data among a predetermined number of ...