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https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-ndbinfo.html
row *************************** Engine: BLACKHOLE Support: YES Comment: /dev/null storage engine (anything you write to it disappears) Transactions: NO XA: NO Savepoints: NO *************************** 5. ndbinfo is a database containing ...
https://dev.mysql.com/doc/refman/5.7/en/nested-join-optimization.html
In some of the following examples, NULL where a table name appears means a row in which NULL is used for each column of that table. For example, t1||t2||NULL indicates a row constructed by concatenating the columns of rows t1 and t2, and NULL for ...
https://dev.mysql.com/doc/refman/5.7/en/json-search-functions.html
Returns NULL if any argument is NULL, or if the path argument does not identify a section of the target document. Returns NULL if any argument is NULL or no paths locate a value in the document. row *************************** id: 1 select_type: ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-limitations-partitioning-keys-unique-keys.html
This section discusses the relationship of partitioning keys with primary keys and unique keys. The rule governing this relationship can be expressed as follows: All columns used in the partitioning expression for a partitioned table must be part ...
https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html
If explicit_defaults_for_timestamp is disabled, the server enables the nonstandard behaviors and handles TIMESTAMP columns as follows: TIMESTAMP columns not explicitly declared with the NULL attribute are automatically declared with the NOT NULL ...
https://dev.mysql.com/doc/refman/5.7/en/create-table.html
NOT NULL | NULL If neither NULL nor NOT NULL is specified, the column is treated as though NULL had been specified. In MySQL 5.7, only the InnoDB, MyISAM, and MEMORY storage engines support indexes on columns that can have NULL values. In other ...| ...
https://dev.mysql.com/doc/refman/5.7/en/subquery-optimization-with-exists.html
This section discusses these optimizations, particularly with regard to the challenges that NULL values present. That is, the “pushdown” strategy works as long as both of these conditions are true: outer_expr and inner_expr cannot be NULL.
https://dev.mysql.com/doc/refman/5.7/en/derived-tables.html
row *************************** id: 1 select_type: PRIMARY table: <derived2> partitions: NULL type: system possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 1 filtered: 100.00 Extra: NULL *************************** 2. row ... A derived ...
https://dev.mysql.com/doc/refman/5.7/en/glossary.html
It provides useful information for the query optimizer, because the column is known to be not null and with unique values. A column can be subject to a unique constraint, a NOT NULL constraint, or both. See Also cardinality, foreign key, index, NOT ... These terms are commonly used in information about the MySQL database ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-range.html
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 range. Ranges should be contiguous but not overlapping, and are defined using the ...