The difference between null and (null in mysql

The difference between NULL and (NULL) in MySQL is as follows: NULL represents an unknown value, while (NULL) represents an explicit null value. NULL occupies no storage space, while (NULL) occupies one byte. NULL is not equal to any value, while (NULL) is equal to itself. NULL is used to represent missing or inapplicable data, while (NULL) is used to explicitly set a field to null.

The difference between NULL and (NULL) in MySQL

##null and (NULL) is a special value in MySQL that represents a null value, but there are subtle differences between them.

NULL represents an unknown value, that is, no value is stored for this field in the database. It is a special reserved word used to indicate missing or inapplicable data.

(NULL) is also a special value, but it represents a clear null value, that is, the database intentionally sets the field to null. It is essentially the same as NULL, but it is surrounded by parentheses, indicating that it is semantically different from other null values.

Main differences

• Semantics: NULL represents an unknown value, while (NULL) represents an explicit null value.
• Storage space: NULL will not occupy any storage space, while (NULL) will occupy one byte of storage space.
• Comparison: NULL is not equal to any value, including itself, while (NULL) is equal to itself.

Usage scenarios

• NULL: is used to represent missing or inapplicable data.
• (NULL): Used to explicitly set a field to NULL to distinguish it from other null values ​​(such as NULL), or to force a field to be converted to NULL.

Example

<code class="sql">SELECT * FROM table_name WHERE column_name IS NULL;  -- 查找具有未知值的记录
SELECT * FROM table_name WHERE column_name = (NULL); -- 查找明确设置为空值的记录</code>

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