SQL SELECT NULL

The SQL SELECT statement is a fundamental query used to retrieve data from a database. However, what happens when you want to retrieve records that have a NULL value in a certain column? That’s where the SQL SELECT NULL clause comes into play. In this guide, we’ll explore how to use the SELECT NULL statement effectively to query for records with NULL values, understand its syntax, and examine practical examples to demonstrate its usage in various scenarios. By the end, you’ll have a solid understanding of how to harness the power of NULL to extract the information you need from your database.

When we are inserting the data in the tables, it is possible that data for some fields are not available. Instead of adding garbage values to these fields, NULL is inserted in the fields.

Hence NULL represents a column field in the table with no value. NULL is not a datatype like “int”, “char”. Also, arithmetic operations on NULL values will result in NULL. Take this example, if we do 81 – NULL. It will result in NULL.

The word NULL is used to describe a missing value in SQL. In a table, a NULL value is a value in a field that appears to be empty. A field with a NULL value is the same as one that has no value. It’s important to grasp the difference between a NULL value and a zero value or a field of spaces.

Syntax

SELECT column1, column2, ...
FROM table_name
WHERE column_name IS NULL;

Example of SQL SELECT NULL

Example 1: Finding records with NULL values in a specific column

-- Create the table
CREATE TABLE students (
    student_id INT PRIMARY KEY,
    student_name VARCHAR(50),
    age INT
);

-- Insert some sample data with NULL values
INSERT INTO students (student_id, student_name, age) VALUES
(1, 'John Doe', 25),
(2, 'Jane Smith', NULL),
(3, 'Mike Johnson', 30),
(4, NULL, 28);

-- Query to select records with NULL values in the 'age' column
SELECT *
FROM students
WHERE age IS NULL;

Output

| student_id | student_name | age |
|------------|--------------|-----|
| 2          | Jane Smith   | NULL|
| 4          | NULL         | 28  |

Example 2: Retrieving records with NULL values in multiple columns

-- Query to select records with NULL values in either 'student_name' or 'age' column
SELECT *
FROM students
WHERE student_name IS NULL OR age IS NULL;

Output

| student_id | student_name | age |
|------------|--------------|-----|
| 2          | Jane Smith   | NULL|
| 4          | NULL         | 28  |

Conclusion

In conclusion, the NULL statement is a powerful tool for querying databases to retrieve records that contain NULL values in specific columns. By using the IS NULL condition within the WHERE clause, you can efficiently filter your results to include only those rows where the specified column lacks a value.

Understanding how to utilize SQL SELECT NULL allows database administrators and developers to effectively manage data integrity and handle situations where missing or unknown values are present in their datasets. Whether it’s identifying incomplete data entries or performing data quality checks, SQL SELECT NULL provides a straightforward mechanism for extracting pertinent information from databases.

By mastering the usage of SQL SELECT NULL, you can enhance your ability to perform data analysis, troubleshoot data quality issues, and develop more robust database applications. It’s a valuable skill for anyone working with relational databases, enabling them to harness the full potential of SQL in managing and querying data effectively.

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