An empty cell is called NULL
NULL means the database has no value there — not zero, not an empty word, just nothing recorded. Because there's nothing to compare, = doesn't work on it. You write IS NULL to find the empty cells, or IS NOT NULL to skip them.
A tiny example
In plain English: Show me the names of the students who have no nickname recorded.
SELECT name
FROM students
WHERE nickname IS NULL;What comes back
| name |
|---|
| Mia |
| Otto |
Mia and Otto are the only students with nothing recorded in the nickname column.
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