Does specifying a foreign key make it an index?

Question

I have a table T with a primary key id and foreign key f. Is f automatically indexed when it is specified as a foreign key? Do I need explicitly add an index for f ?

Answer 1

No index is created so yes, you need add explicitly add an index.

Edited to add... I probably ought to add that the source table/column for the data in table T must have a unique index. If you try and make an FK to a column that isn't a unique index (either as a PK or with a UNIQUE constraint), the FK can't be created.

Answer 2

No, it is a constraint, not an index.

see Are foreign keys indexed automatically in SQL Server?