select * from doctor ;

+----+-----------------+
| id | name            |
+----+-----------------+
|  1 | Fred Flintstone |  They retrained :-)
|  2 | Barney Rubble   |
+----+-----------------+

select * from specialization ;

+----+------------+
| id | name       |
+----+------------+
| 33 | Neurology  |
| 44 | Psychiatry |
| 55 | Radiology  |
+----+------------+

select * from doctor_specialization ;

+--------+---------+
| doc_id | spec_id |
+--------+---------+
|      1 |      33 |
|      2 |      55 |
+--------+---------+

primary key ( doc_id, spec_id )
foreign key ( doc_id ) references doctor ( id )
foreign key ( spec_id ) references specialization (id )

create index i_ds_spec
on doctor_specialization ( spec_id, doc_id ) ;