Following are the differences between union and join in relational database engines.
A union returns the results of two different queries as a single recordset and A join allows you to relate similar data in different tables.
| UNION | JOIN |
|---|---|
| UNION puts lines from queries after each other, | JOIN makes a cartesian product and subsets it |
| Union Operation is combined result of the Vertical Aggregate of the rows | JOIN Operation is combined result of the Horizontal Aggregate of the Columns |
| Union combines rows | JOIN links the rows |
| Performed only on two similar structures | Performed only on two dissimilar structures also |
| A union returns the results of two different queries as a single recordset. | A join allows you to relate similar data in different tables. |
Visual depiction of a join. Table A and B’s columns are combined into a single result:
Visual depiction of a union columns aren’t combined to create results, rows are combined:
