If you join a table to itself, what kind of join are you using?
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Self Join
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Selective Join.
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Outer Join
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You can't join a table to itself.
A self-join occurs when a table is joined to itself, typically to compare rows within the same table or establish hierarchical relationships. The table appears in both the FROM and JOIN clauses, often with different aliases. Option B's 'Selective Join' is not standard SQL terminology. Option C (Outer Join) preserves unmatched rows but isn't specific to self-joins.
Joining a table to itself, typically by aliasing it as two different names, is called a self join — commonly used to compare rows within the same table (e.g., an employee table joined to itself to find each employee's manager). It's a normal SQL technique, not an outer join or an invalid operation.