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https://dev.mysql.com/doc/refman/5.7/en/partitioning-handling-nulls.html
Partitioning in MySQL does nothing to disallow NULL as the value of a partitioning expression, whether it is a column value or the value of a user-supplied expression. Even though it is permitted to use NULL as the value of an expression that must ...We can verify this behavior by examining the effects on the file system of creating a table partitioned by HASH and populating it with a record containing appropriate ...
https://dev.mysql.com/doc/refman/5.7/en/working-with-null.html
The NULL value can be surprising until you get used to it. Conceptually, NULL means “a missing unknown value” and it is treated somewhat differently from other values. In MySQL, 0 or NULL means false and anything else means true. This special ...
https://dev.mysql.com/doc/refman/5.7/en/problems-with-null.html
The concept of the NULL value is a common source of confusion for newcomers to SQL, who often think that NULL is the same thing as an empty string ''. For example, the following statements are completely different: mysql> INSERT INTO my_table ...
https://dev.mysql.com/doc/refman/5.7/en/is-null-optimization.html
MySQL can perform the same optimization on col_name IS NULL that it can use for col_name = constant_value. For example, MySQL can use indexes and ranges to search for NULL with IS NULL. This optimization does not occur in cases when the column ...
https://dev.mysql.com/doc/refman/5.7/en/null-values.html
The NULL value means “no data.” NULL can be written in any lettercase. Treatment of \N as a synonym for NULL in SQL statements is deprecated as of MySQL 5.7.18 and is removed in MySQL 8.0; use NULL instead. Be aware that the NULL value is ...
https://dev.mysql.com/doc/refman/5.7/en/comparison-operators.html
Table 12.4 Comparison Operators Name Description > Greater than operator >= Greater than or equal operator < Less than operator <>, != Not equal operator <= Less than or equal operator <=> NULL-safe equal to operator = Equal operator BETWEEN ...
https://dev.mysql.com/doc/refman/5.7/en/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/doc/refman/5.7/en/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'); -> ...For functions that operate on string positions, the first position is ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-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. Where no value is provided by the ... The ...
https://dev.mysql.com/doc/refman/5.7/en/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 ...