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Databases Querying Relational Databases Subqueries Review and Practice

Posted by Özgür Yildirim
Özgür Yildirim
4,088 Points

Difference between UNION and UNION ALL for the second practice question?

The answer changes depending on whether we use the UNION or UNION ALL operator to bring together the loans_north with the loans_south table. There is approximately one record more for each patron, except for Craig. He did not loan any book from any library. I do not understand why there should be one more record if we do UNION ALL. Does anyone know the difference?