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https://dev.mysql.com/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/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/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/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/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 sorting with ORDER BY, NULL values sort before ...
https://dev.mysql.com/null-mysql-store-result.html
It is possible for mysql_store_result() to return NULL following a successful call to mysql_query(). When this happens, it means one of the following conditions occurred: There was a malloc() failure (for example, if the result set was too large).
https://dev.mysql.com/group-by-modifiers.html
These rows have the country and products columns set to NULL. This row has the year, country, and products columns set to NULL. The NULL indicators in each super-aggregate row are produced when the row is sent to the client. For any column in the ...
https://dev.mysql.com/create-index.html
If a table contains no primary key, InnoDB automatically promotes the first UNIQUE NOT NULL index to the primary key. This is not supported for UNIQUE NOT NULL indexes that have functional key parts. A UNIQUE index permits multiple NULL values for ... CREATE [UNIQUE | FULLTEXT | SPATIAL] INDEX index_name [index_type] ON tbl_name (key_part,...) [index_option] [algorithm_option | lock_option] ...
https://dev.mysql.com/miscellaneous-functions.html
There are multiple ways to cause MySQL to accept the query: Alter the table to make name a primary key or a unique NOT NULL column. (This technique is inapplicable if NULL must be permitted as a valid name value.) Use ANY_VALUE() to refer to ...The ...
https://dev.mysql.com/comparison-operators.html
Whether a value is not within a range of values !=, <> Not equal operator NOT IN() Whether a value is not within a set of values NOT LIKE Negation of simple pattern matching STRCMP() Compare two strings Comparison operations result in a value of 1 ...Strings are automatically converted to numbers and numbers to strings as ...
Document created the 26/06/2006, last modified the 26/10/2018
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