Which describes an Outer Join?

Which describes an Outer Join?

• A. A cross join with all combinations.
• B. A self join on the same table.
• C. A type of join where all records from one table and related records from a related table appear in a result set.
• D. A type of join where only matched records are returned.

Answer: (C)

Outer join preserves rows from one side of the relationship and brings in matching rows from the other side, filling with NULLs when there is no match. This is what the description is getting at: you get all records from one table plus the related data from the other table when available, and you still see those rows even if there’s no related entry. That’s why it can be a left, right, or full outer join, depending on which side you want to preserve. For example, selecting all employees and their departments with a left join would show every employee, and department details where available; if an employee isn’t assigned to a department, the department fields come back as NULL. This contrasts with a cross join (which returns every possible pair of rows), a self join (joining a table to itself, which may be inner or outer but isn’t defined by the outer-join behavior), or an inner join (which returns only rows that have matches on both sides).

Outer join preserves rows from one side of the relationship and brings in matching rows from the other side, filling with NULLs when there is no match. This is what the description is getting at: you get all records from one table plus the related data from the other table when available, and you still see those rows even if there’s no related entry. That’s why it can be a left, right, or full outer join, depending on which side you want to preserve.

For example, selecting all employees and their departments with a left join would show every employee, and department details where available; if an employee isn’t assigned to a department, the department fields come back as NULL. This contrasts with a cross join (which returns every possible pair of rows), a self join (joining a table to itself, which may be inner or outer but isn’t defined by the outer-join behavior), or an inner join (which returns only rows that have matches on both sides).