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https://dev.mysql.com/doc/refman/8.4/en/date-and-time-type-syntax.html
Also, any TIMESTAMP not explicitly declared as NOT NULL permits NULL values. You can also set any TIMESTAMP column to the current date and time by assigning it a NULL value, unless it has been defined with the NULL attribute to permit NULL values.
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-virtual-table.html
CREATE TABLE `t1` ( `a` int(11) DEFAULT NULL, `b` int(11) DEFAULT NULL, `c` int(11) GENERATED ALWAYS AS (5) VIRTUAL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4; However, metadata for such a column does appear in the INNODB_COLUMNS table. The ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-tables-table.html
Not all storage engines update this time, in which case, the value is always NULL. For views, most TABLES columns are 0 or NULL except that TABLE_NAME indicates the view name, CREATE_TIME indicates the creation time, and TABLE_COMMENT says VIEW. The ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-optimize-tablespace-page-allocation.html
By default, when additional space is required, InnoDB allocates pages to the tablespace and physically writes NULLs to those pages. You can disable innodb_extend_and_initialize on Linux systems to avoid physically writing NULLs to newly allocated ...
https://dev.mysql.com/doc/refman/8.4/en/mysql-cluster-ndbinfo-dict-obj-tree.html
The dict_obj_tree table provides a tree-based view of table information from the dict_obj_info table. This is intended primarily for use in testing, but can be useful in visualizing hierarchies of NDB database objects. This means that you must know ...
https://dev.mysql.com/doc/refman/8.4/en/non-typed-operators.html
->> Return value from JSON column after evaluating path and unquoting the result; equivalent to JSON_UNQUOTE(JSON_EXTRACT()). / Division operator := Assign a value = Assign a value (as part of a SET statement, or as part of the SET clause in an ...
https://dev.mysql.com/doc/refman/8.4/en/optimizer-hints.html
row *************************** id: 1 select_type: SIMPLE table: t1 partitions: NULL type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 256 filtered: 100.00 Extra: Using filesort The USE INDEX, FORCE INDEX, and IGNORE INDEX index ... One means of control over optimizer strategies is to set the optimizer_switch system variable (see Section 10.9.2, “Switchable ...
https://dev.mysql.com/doc/refman/8.4/en/other-vendor-data-types.html
To facilitate the use of code written for SQL implementations from other vendors, MySQL maps data types as shown in the following table. These mappings make it easier to import table definitions from other database systems into MySQL. If you create ...
https://dev.mysql.com/doc/refman/8.4/en/outer-join-optimization.html
If there is a row in A that matches the WHERE clause, but there is no row in B that matches the ON condition, an extra B row is generated with all columns set to NULL. For a LEFT JOIN, if the WHERE condition is always false for the generated NULL ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-ndb-sync-excluded-objects-table.html
row *************************** SCHEMA_NAME: NULL NAME: lg1 TYPE: LOGFILE GROUP REASON: Injected failure *************************** 2. row *************************** SCHEMA_NAME: NULL NAME: ts1 TYPE: TABLESPACE REASON: Injected failure ... This ...