SQL TutorialLesson 33Free preview

SQL Union All

This lesson is part of SQL · All levels

Summary

UNION ALL incorporates the query results exactly like UNION, but maintains a duplicate line. Since there is no need to check duplicates, UNION ALL is generally faster. Use UNION ALL if duplicate is not a problem or is actually needed.

Key points

Union All is union without duplicate deletion.
It's usually faster because it goes through the process of deduplication.
The resulting line number is the total line of all queries combined.
It's a good idea to combine period data that's definitely not overlapping.
UNION is usually used when unique results are needed.

Full lesson

Code examples and quizzes

Full lessons, code examples, and quizzes are available to subscribers. 5 questions.