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7. NULL Values: Missing Data Done Right

7.2 How to Find Missing Values with IS NULL and IS NOT NULL

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Why. You must find missing rows before you fix or report them.

What. Use IS NULL and IS NOT NULL — special tests for missing.

How. WHERE note IS NULL / WHERE note IS NOT NULL

Steps

  1. Count rows with missing notes.
  2. List rows that have a note.
  3. Same idea on interview_mini tickets.priority.

Examples

Example 1 · dataset: raja_coffee

SELECT COUNT(*) AS missing_notes
FROM orders
WHERE note IS NULL;

Output

missing_notes
22

Meaning. How many orders have no note.

Example 2 · dataset: interview_mini

SELECT ticket_id, agent, priority
FROM tickets
WHERE priority IS NULL;

Output

ticket_idagentpriority
6James

Meaning. Tickets with unknown priority.

Ravindra Bagale's Tip

IS NULL reads like English — keep using it; do not invent = NULL.