This combination of letters has some eccentric rules.
At times the CH is pronounced as a K. Such as in school, cholera, chasm,
charisma, chemo, Christ, Christian, chrome, chronic, chronicle, and others.
At times the CH is pronounced as SH. Mostly in words of French origin: Such
as Champaign, chandelier, chauffeur, chef, parachute, and chute.
On some the H in CH is silent: Such as chinch where in the first CH, the H
is silent but not in the second CH. In yacht the CH is silent.
Choir is odd in that it sounds exactly as quire. It would be more likely to
be spelled as kwire.
Happily is that most cases CH gets pronounced as CH. How normal is that?
This one takes on two sets of rules.
in words such as occurrence, occur, occasion, and others CC is pronounced
as a K.
In words such as success, succeed, and eccentric, and others the first C
is pronounced as a K and the second C as an S.