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Task 26:

Difference between UNION and UNION ALL

What is the difference between UNION and UNION ALL?

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

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

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

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

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