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https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html
ABS(X) Returns the absolute value of X, or NULL if X is NULL. An implication of this is that ABS(-9223372036854775808) produces an error because the result cannot be stored in a signed BIGINT value. mysql> SELECT ABS(2); -> 2 mysql> SELECT ABS(-32); ...
https://dev.mysql.com/doc/refman/5.7/en/merge-table-advantages.html
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 one. MERGE tables can help you solve the following problems: Easily manage a set of log ...
https://dev.mysql.com/doc/refman/5.7/en/monitor-alter-table-performance-schema.html
WORK_ESTIMATED is calculated using a formula that takes into account all of the work that ALTER TABLE performs, and may be revised during ALTER TABLE processing. You can monitor ALTER TABLE progress for InnoDB tables using Performance Schema. There ...
https://dev.mysql.com/doc/refman/5.7/en/mrr-optimization.html
The accessed rows are packed into packages and sent back to the central node. 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 ...
https://dev.mysql.com/doc/refman/5.7/en/multiple-data-directories.html
You can unpack such a distribution into a temporary location, then copy it data directory to where you are setting up the new instance. Each MySQL Instance on a machine should have its own data directory. There are different methods of setting up a ...
https://dev.mysql.com/doc/refman/5.7/en/multiple-server-clients.html
Start the client with --protocol=TCP to connect using TCP/IP, --protocol=SOCKET to connect using a Unix socket file, --protocol=PIPE to connect using a named pipe, or --protocol=MEMORY to connect using shared memory. For TCP/IP connections, you may ...
https://dev.mysql.com/doc/refman/5.7/en/multiple-tables.html
The pet table keeps track of which pets you have. If you want to record other information about them, such as events in their lives like visits to the vet or when litters are born, you need another table. What should this table look like? It needs ...
https://dev.mysql.com/doc/refman/5.7/en/myisam-key-cache.html
That is, it reads from the cache or writes into it rather than reading from or writing to disk. To minimize disk I/O, the MyISAM storage engine exploits a strategy that is used by many database management systems. It employs a cache mechanism to ...
https://dev.mysql.com/doc/refman/5.7/en/myisam-maintenance-schedule.html
Alternatively, if you can stop the mysqld server for a while, change location into the data directory and use this command while the server is stopped: $> myisamchk -r -s --sort-index --myisam_sort_buffer_size=16M */*.MYI . It is a good idea to ...
https://dev.mysql.com/doc/refman/5.7/en/myisam-storage-engine.html
MyISAM supports concurrent inserts: If a table has no free blocks in the middle of the data file, you can INSERT new rows into it at the same time that other threads are reading from the table. MyISAM is based on the older (and no longer available) ...