SQL Interview Questions #26: Difference between UNION and UNION ALL

Task 26:

What is the difference between UNION and UNION ALL?

UNION joins only those records that have matches, and UNION ALL joins all records without exception.

UNION removes NULL values when combining data, while UNION ALL leaves them.

When combining data, UNION ALL returns all rows, and UNION returns only unique rows.

In UNION, the list of fields of the combined data must be identical, but in UNION ALL this is not necessary.

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