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https://dev.mysql.com/timestamp-initialization.html
In addition, if the explicit_defaults_for_timestamp system variable is disabled, you can initialize or update any TIMESTAMP (but not DATETIME) column to the current date and time by assigning it a NULL value, unless it has been defined with the NULL ... TIMESTAMP and DATETIME columns can be automatically initializated and updated to the current date and time (that is, the current ...
https://dev.mysql.com/files-table.html
The value is NULL for all data files except for predefined system tablespace data files. A NULL value for a predefined system tablespace data file indicates that a file size limit was not defined explicitly. For NDB: For NDB Cluster Disk Data files, ... The FILES table provides information about the files in which MySQL tablespace data is ...
https://dev.mysql.com/string-functions.html
Also, if strict SQL mode is enabled, the result from CHAR() becomes NULL. mysql> SELECT CONCAT_WS(',','First name','Second name','Last Name'); -> 'First name,Second name,Last Name' mysql> SELECT CONCAT_WS(',','First name',NULL,'Last Name'); -> ...
https://dev.mysql.com/explain-output.html
The value can be NULL if the row refers to the union result of other rows. If this column is NULL (or undefined in JSON-formatted output), there are no relevant indexes. If key is NULL, MySQL found no index to use for executing the query more ...
https://dev.mysql.com/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/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/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/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/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 8.0, only the InnoDB, MyISAM, and MEMORY storage engines support indexes on columns that can have NULL values. In other ...
https://dev.mysql.com/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.
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