The difference between null value and null in sql

In SQL, NULL represents unknown data, while null represents an unassigned value. The difference between NULL and null values ​​lies in semantic meaning (NULL is unambiguously missing, and null values ​​do not require semantics), performance efficiency (NULL processing is more efficient), and query results (NULL comparison results are unpredictable). Determine NULL and null values ​​via IS NULL, IS NOT NULL, or COALESCE. Best practices are to explicitly use NULL to indicate missing data, avoid using null values, and handle NULL values ​​wisely.

The difference between NULL and null values ​​in SQL

In SQL, NULL and null values ​​are different concepts .

Null value refers to a field or column that has not yet been assigned a value. When data is retrieved from a table, null values ​​appear in a specific way, depending on the database management system (DBMS). For example, in MySQL, null values ​​appear as the empty string, 0, or NULL, depending on the field's data type.

NULL is a special value that clearly indicates that the value of the field is unknown or does not exist. It differs from the null value in that it indicates an actual absence in the data rather than that a value has not yet been assigned.

Meaning of the Difference

The difference between NULL and null values ​​is significant:

• Data Integrity:NULL is used to represent missing or unknown data, and null values ​​do not require any semantics.
• Performance: Some DBMS handle NULL values ​​more efficiently than NULL values.
• Query results: When comparing NULL values ​​to other values, the results may be unpredictable.

Judge NULL and empty values

In SQL, you can use the following method to determine whether a value is NULL or empty:

• IS NULL: Returns a Boolean value indicating whether the value is NULL.
• IS NOT NULL: Returns a Boolean value indicating whether the value is not NULL.
• COALESCE: Returns the first non-NULL value, or the specified default value if all values ​​are NULL.

Best Practices

When using NULL and null values ​​in SQL, you should follow the following best practices:

• Explicitly use NULL to represent missing or unknown data.
• Avoid using null values ​​as it may cause data integrity issues.
• Handle NULL values ​​wisely in queries, consider using the IS NULL, IS NOT NULL, or COALESCE functions.

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