Handle NULLs in SQL

Handle NULLs in SQL

In this tutorial, we are going to discuss about how to handle NULLs in SQL. Handling NULL values in SQL is essential to ensure data integrity and accurate query results. NULL represents a missing or unknown value, and it can behave differently from other values in SQL.

What are Null Values?

Null values in MySQL indicate the absence of a value in a column. Unlike an empty string or zero, null is not a valid data value and typically represents missing or unknown information. Columns in a MySQL table can be defined to allow or disallow null values based on the data requirements.

Handle NULLs in SQL

Here are some common methods to handle NULLs:

Handling Null Values

1. Allowing Null Values in Columns:

When defining a table, you can specify whether a column allows null values or not. This is done using the NULL attribute in the column definition.

CREATE TABLE students (
    id INT,
    email VARCHAR(255) NULL,
    name VARCHAR(255)
);

In the above example, email allows null values, while name does not.

2. Checking for Null Values:

To check if a column contains null values, you can use the IS NULL or IS NOT NULL condition in a WHERE clause.

SELECT * FROM students WHERE email IS NULL;

This query retrieves rows where email contains null values.

3. Using IS NULL and IS NOT NULL to Check for NULL

To filter records based on whether a column is NULL or not:

SELECT *
FROM table_name
WHERE column_name IS NULL;
SELECT *
FROM table_name
WHERE column_name IS NOT NULL;

4. Using COALESCE to Replace NULL

COALESCE returns the first non-NULL value in a list:

SELECT COALESCE(column_name, 'default_value') AS column_name
FROM table_name;

5. Using IFNULL or NVL to Replace NULL

These functions provide similar functionality to COALESCE but are specific to certain SQL databases:

1. MySQL

SELECT IFNULL(column_name, 'default_value') AS column_name
FROM table_name;

2. Oracle

SELECT NVL(column_name, 'default_value') AS column_name
FROM table_name;

6. Using CASE Statements

CASE can provide more complex conditional logic:

SELECT
  CASE
    WHEN column_name IS NULL THEN 'default_value'
    ELSE column_name
  END AS column_name
FROM table_name;

7. Handling NULL in Aggregations

Aggregations like SUM, AVG, MAX, etc., automatically ignore NULL values. To include NULL values, you can use COALESCE or similar functions:

SELECT SUM(COALESCE(column_name, 0)) AS total
FROM table_name;

8. NULL-safe Comparisons

  • MySQL supports the <=> operator for NULL-safe comparisons:
SELECT *
FROM table_name
WHERE column_name <=> NULL;

9. Sorting with NULLS FIRST or NULLS LAST

Some databases support sorting options for NULL values:

SELECT *
FROM table_name
ORDER BY column_name ASC NULLS LAST;

These techniques help manage NULL values efficiently, ensuring they don’t lead to unexpected results in your queries.

That’s all about the how to Handle NULLs in SQL. If you have any queries or feedback, please write us at contact@waytoeasylearn.com. Enjoy learning, Enjoy SQL..!!

Handle NULLs in SQL
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