What does null mean in mysql?

NULL in MySQL is a special placeholder that represents an unknown or non-existent value. It is different from the empty string or 0, and is not equal to itself or any other value. To handle NULL, you can use the special operators IS NULL and IS NOT NULL. Additionally, functions such as COALESCE(), IFNULL(), and NVL() can help handle NULL values. Best practices include avoiding NULL, using default values, and using explicit operators to compare NULL values.

NULL in MySQL

In the MySQL database, NULL is a special placeholder that represents a Unknown or non-existent value. Unlike other values ​​such as the empty string ("") or 0, NULL means that the field has no value.

When to use NULL

NULL is typically used in the following situations:

• When the data has not been collected or is not available.
• When the data is not part of a specific record.
• When the data type does not allow the storage of a specific value (for example, an integer does not allow the storage of a string).

Compare NULL

Unlike other values, NULL is neither equal to itself nor to any other value. This means that when checking for NULL using the regular comparison operators (=, !=, <, >, <=, >=), the result is always unknown or undefined.

To handle this situation, MySQL provides the special operators IS NULL and IS NOT NULL.

• IS NULL The return result is NULL
• IS NOT NULL The return result is not NULL

Handling NULL

When dealing with NULL values, you can use the following functions:

• COALESCE(expr1, expr2, ...) : Returns the first non-NULL expression.
• IFNULL(expr1, expr2): If expr1 is NULL, return expr2; otherwise, return expr1.
• NVL(expr1, expr2): Same as IFNULL().

Best Practices

When using NULL, please pay attention to the following best practices:

• Avoid using NULL as much as possible, Because it makes data incomplete and queries complex.
• For fields that allow NULL, use appropriate default values.
• Explicitly use IS NULL and IS NOT NULL to compare NULL values.

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