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https://dev.mysql.com/doc/refman/8.0/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 ...
https://dev.mysql.com/doc/refman/8.0/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/8.0/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/8.0/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/8.0/en/null-values.html
The NULL value means “no data.” NULL can be written in any lettercase. Be aware that the NULL value is different from values such as 0 for numeric types or the empty string for string types. For text file import or export operations performed ...
https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html
This section describes the functions that can be used to manipulate temporal values. See Section 13.2, “Date and Time Data Types”, for a description of the range of values each date and time type has and the valid formats in which values may be ...
https://dev.mysql.com/doc/refman/8.0/en/string-functions.html
For functions that operate on string positions, the first position is numbered 1. For functions that take length arguments, noninteger arguments are rounded to the nearest integer. ASCII(str) Returns the numeric value of the leftmost character of ...
https://dev.mysql.com/doc/refman/8.0/en/group-by-modifiers.html
The GROUP BY clause permits a WITH ROLLUP modifier that causes summary output to include extra rows that represent higher-level (that is, super-aggregate) summary operations. ROLLUP thus enables you to answer questions at multiple levels of ...
https://dev.mysql.com/doc/refman/8.0/en/switchable-optimizations.html
Its value is a set of flags, each of which has a value of on or off to indicate whether the corresponding optimizer behavior is enabled or disabled. This variable has global and session values and can be changed at runtime. To see the current set of ...
https://dev.mysql.com/doc/refman/8.0/en/miscellaneous-functions.html
The function return value and type are the same as the return value and type of its argument, but the function result is not checked for the ONLY_FULL_GROUP_BY SQL mode. As a result, the address value for rows within each name group is ...