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https://dev.mysql.com/doc/refman/5.7/en/range-optimization.html
AND key_partN cmp constN; Here, const1, const2, … are constants, cmp is one of the =, <=>, or IS NULL comparison operators, and the conditions cover all index parts. For a BTREE index, an interval might be usable for conditions combined with AND, ... The range access method uses a single index to retrieve a subset of table rows that are contained within one or several index value ...
https://dev.mysql.com/doc/refman/5.7/en/show-columns.html
Collation The collation for nonbinary string columns, or NULL for other columns. The value is YES if NULL values can be stored in the column, NO if not. (A UNIQUE index permits multiple NULL values, but you can tell whether the column permits NULL ... SHOW [FULL] {COLUMNS | FIELDS} {FROM | IN} tbl_name [{FROM | IN} db_name] [LIKE 'pattern' | WHERE expr] SHOW COLUMNS displays information about the columns in a given ...
https://dev.mysql.com/doc/refman/5.7/en/alter-table.html
Running ALTER TABLE tbl_name ENGINE=INNODB on an existing InnoDB table performs a “null” ALTER TABLE operation, which can be used to defragment an InnoDB table, as described in Section 14.12.4, “Defragmenting a Table”. The outcome of ...
https://dev.mysql.com/doc/refman/5.7/en/select-into.html
If the FIELDS ESCAPED BY character is empty, no characters are escaped and NULL is output as NULL, not \N. INTO form of SELECT enables a query result to be stored in variables or written to a file: SELECT ... Column and line terminators can be ...
https://dev.mysql.com/doc/refman/5.7/en/audit-log-reference.html
Return value: The password string for success (up to 766 bytes), or NULL and an error for failure. Each element in the returned array is an event represented as a JSON hash, with the exception that the last element may be a JSON null value to ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-row-format.html
An SQL NULL value reserves one or two bytes in the record directory. An SQL NULL value reserves zero bytes in the data part of the record if stored in a variable-length column. Reserving fixed space for NULL values permits columns to be updated in ... The row format of a table determines how its rows are physically stored, which in turn can affect the performance of queries and DML ...
https://dev.mysql.com/doc/refman/5.7/en/spatial-relation-functions-mbr.html
MBRCoveredBy() handles its arguments as follows: If either argument is NULL or an empty geometry, the return value is NULL. MBRCovers() handles its arguments as follows: If either argument is NULL or an empty geometry, the return value is NULL.
https://dev.mysql.com/doc/refman/5.7/en/scalar-subqueries.html
A scalar subquery is a simple operand, and you can use it almost anywhere a single column value or literal is legal, and you can expect it to have those characteristics that all operands have: a data type, a length, an indication that it can be ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-processlist-table.html
row *************************** ID: 5 USER: event_scheduler HOST: localhost DB: NULL COMMAND: Daemon TIME: 137 STATE: Waiting on empty queue INFO: NULL *************************** 2. row *************************** ID: 9 USER: me HOST: ... Note The ...
https://dev.mysql.com/doc/refman/5.7/en/getting-information.html
To find out which database is currently selected, use the DATABASE() function: mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | menagerie | +------------+ If you have not yet selected any database, the result is NULL. What ...