One of the common themes in cop movies/stories is the long term ‘partnering’ of two detectives (or sometime uniformed officers). Think Riggs/Murtaugh, Crockett/Tubbs, Cagney/Lacey etc.
Do police departments generally pair up cops with a long term partner who they work with exclusively?
The answer, as it so often does, varies by location.
Some Spanish police forces tend to set up partnerships for patrol cops but not for other positions; Guardia Civiles usually partner up, but this applies only to grades below Sergeant (the Civiles have a military structure, it’s complicated). Other forces specifically randomize partnering, in order to avoid the kind of situation where one guy’s loyalty to his partner becomes greater than his loyalty to the job/the force/etc. None of the Spanish police forces has a grade called “Detective”; American Detectives usually get translated as “Inspector”, but in the only Spanish police force I know which has Inspectores (the Nacionales), they don’t work partnered.
I can’t answer for other countries, and we have so many forces between national, regional and local levels that I can’t swear there aren’t Inspectores anywhere else.
Late: at the beginning of the movie Belle Epoque you see two Guardia Civiles walking along their patrol route. From their conversation, they are son- and father-in-law. At the end of that scene, the son-in-law shoots and kills his partner. The notion of a Civil murdering his partner is about as unthinkable as that of someone biting his own head off; the shock caused by that was enough to set the mood for the whole movie as “completely absurd”. It is, in fact, a very good representative of Humor del Absurdo, Absurdist Humor.