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https://dev.mysql.com/doc/refman/5.7/en/monitor-alter-table-performance-schema.html
stage/innodb/alter table (log apply index): This stage includes the application of DML log generated while ALTER TABLE was running. stage/innodb/alter table (log apply table): This stage includes the application of concurrent DML log generated while ... You can monitor ALTER TABLE progress for InnoDB tables using Performance ...
https://dev.mysql.com/doc/refman/5.7/en/semijoins.html
Assuming that class_num is a primary key in the class table, duplicate suppression is possible by using SELECT DISTINCT, but it is inefficient to generate all matching rows first only to eliminate duplicates later. WHERE ...); Here, ot_i and it_i ...
https://dev.mysql.com/doc/refman/5.7/en/time-zone-support.html
This includes the values displayed by functions such as NOW() or CURTIME(), and values stored in and retrieved from TIMESTAMP columns. Values for TIMESTAMP columns are converted from the session time zone to UTC for storage, and from UTC to the ...
https://dev.mysql.com/doc/refman/5.7/en/data-size.html
You can get better performance for a table and minimize storage space by using the techniques listed here: Table Columns Row Format Indexes Joins Normalization Table Columns Use the most efficient (smallest) data types possible. MEDIUMINT is often a ... Design your tables to minimize their space on the ...
https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-ndbinfo-cluster-locks.html
The transaction ID (transid column) is the identifier generated by the NDB API for the transaction requesting or holding the current lock. The mode column shows the lock mode; this is always one of S (indicating a shared lock) or X (an exclusive ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-information-schema-temp-table-info.html
The NAME column displays the system-generated name for the temporary table, which is prefixed with “#sql”. The number of columns (N_COLS) is 4 rather than 1 because InnoDB always creates three hidden table columns (DB_ROW_ID, DB_TRX_ID, and ...
https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html
With a nonconstant initializer argument (such as a column name), the seed is initialized with the value for each invocation of RAND(). One implication of this behavior is that for equal argument values, RAND(N) returns the same value each time, and ...ABS(X) Returns the absolute value of X, or NULL if X is ...
https://dev.mysql.com/doc/refman/5.7/en/mrr-optimization.html
The MRR optimization is not supported with secondary indexes created on virtual generated columns. When MRR is used, the Extra column in EXPLAIN output shows Using MRR. Reading rows using a range scan on a secondary index can result in many random ...
https://dev.mysql.com/doc/refman/5.7/en/faqs-cjk.html
You can obtain this information for a column column_name in the table table_name using the following query: SELECT HEX(column_name) FROM table_name; 3F is the encoding for the ? character; this means that ? is the character actually stored in the ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-range.html
While the examples work as shown for purposes of the present discussion, you should keep in mind that tables are extremely likely in practice to have primary keys, unique keys, or both, and that allowable choices for partitioning columns depend on ... A table that is partitioned by range is partitioned in such a way that each partition contains rows for which the partitioning expression value lies within a given ...