MySQL IS NULL Keyword
The IS NULL
keyword in MySQL is used to check whether a column contains a NULL value. It is often employed in conditional statements to filter or identify rows with missing data.
Usage
The IS NULL
keyword is used in SELECT
, UPDATE
, or DELETE
statements to test for NULL values in a specified column. It helps in handling data that might be incomplete or missing.
sql
SELECT column1, column2, ...
FROM table_name
WHERE column_name IS NULL;
In this syntax, column_name IS NULL
checks whether column_name
contains a NULL value.
Examples
1. Basic NULL Check
sql
SELECT *
FROM products
WHERE price IS NULL;
This example retrieves all records from the products
table where the price
column is NULL.
2. Updating NULL Values
sql
UPDATE employees
SET department = 'Unassigned'
WHERE department IS NULL;
Here, any employee records with a NULL department are updated to 'Unassigned'.
3. Deleting Rows with NULL
sql
DELETE FROM orders
WHERE shipment_date IS NULL;
This command removes all entries from the orders
table where the shipment date is missing (NULL).
4. Combining IS NULL and IS NOT NULL
sql
SELECT *
FROM orders
WHERE shipment_date IS NULL OR delivery_date IS NOT NULL;
This example selects records where the shipment date is NULL or the delivery date is not NULL, illustrating the combined use of IS NULL
and IS NOT NULL
.
Tips and Best Practices
- Use IS NULL for precision. Always use
IS NULL
instead of= NULL
to ensure accurate checking for NULL values. Using= NULL
will not yield correct results because, in SQL, NULL represents an unknown value and cannot be equated. - Consider data integrity. Use
IS NULL
to find and handle incomplete data, ensuring data integrity and consistency. - Combine with IS NOT NULL. Pair
IS NULL
withIS NOT NULL
to manage both missing and non-missing data effectively. - Index consideration. Remember that NULL values are not indexed in MySQL, which can lead to full table scans and affect query performance. Be mindful of this, especially in large datasets.