Set operations combine query results vertically or logically, while JOINs connect related columns between datasets.
Complex reporting often requires both row-set comparison and relational matching.
Combine customer IDs from two sources and then retrieve customer details.
SELECT
c.CustomerID,
c.CustomerName
FROM Customers c
INNER JOIN (
SELECT CustomerID
FROM OnlineCustomers
UNION
SELECT CustomerID
FROM BranchCustomers
) x
ON c.CustomerID = x.CustomerID;Used in data migration, reconciliation, enterprise reporting, and master-data management.
- Set operations combine result sets.
- JOIN connects rows through related columns.
- UNION combines rows from multiple queries.
- INTERSECT finds common rows.
- EXCEPT finds rows missing from the second result.
How are JOINs different from set operations?
JOINs combine columns horizontally using relationships, while set operations combine compatible result rows vertically.
Can JOIN and UNION be used together?
Yes. A UNION result can be treated as a derived dataset and JOINed with another table.