5.2 — NULL Value Solutions

What You'll Learn

• What NULL means in SQL
• How to filter, replace, and work with missing values
• Excel blanks vs. SQL NULL

What is NULL?

In SQL, NULL means missing or unknown data—similar to a blank cell in Excel.

Filtering for NULL Values

Find rows with missing Amount:

SELECT *
FROM sales
WHERE Amount IS NULL;

Exclude rows with missing Amount:

SELECT *
FROM sales
WHERE Amount IS NOT NULL;

Replacing NULL Values

Use COALESCE() to provide a default value if a column is NULL:

SELECT Product, COALESCE(Amount, 0) AS Amount_Filled
FROM sales;

• This will show 0 instead of NULL for missing Amounts.

Using CASE for NULL Handling

You can also use CASE to handle NULL:

SELECT Product,
  CASE
    WHEN Amount IS NULL THEN 'Missing'
    ELSE CAST(Amount AS VARCHAR)
  END AS Amount_Status
FROM sales;

Key Points

• NULL is not the same as zero or an empty string.
• Use IS NULL/IS NOT NULL to filter.
• Use COALESCE() or CASE to replace or flag missing values.

Next Steps

Next, you’ll learn about subqueries—using queries inside other queries for dynamic filtering.