Does a SQLite Foreign key automatically have an index?

Even if it is not actually a no-op (a data structure describing the constraint is added to the table), foreign key related statement doesn't create any index on involved columns. Indexes are implicitly created only in the case of PRIMARY KEY and UNIQUE statements. For more details, check it out build.c module on the sqlite source tree: http://www.sqlite.org/cvstrac/rlog?f=sqlite/src/build.c https://www.sqlite.org/src/file?name=src/build.c&ci=tip

In the SQLite Documentation it says:

... "an index should be created on the child key columns of each foreign key constraint"

ie. the index is not automatically created, but you should create one in every instance.