GROUP_CONCAT(letter)
a,Ạ,ạ,Á,á,Ã,ã,Ả,ả,À,à,A
Ẵ,ắ,Ắ,ặ,Ặ,ẵ,Ẳ,ẳ,Ằ,ằ,Ă,ă
Ẫ,ấ,Ấ,ậ,Ậ,ẫ,Ẩ,â,Â,ầ,Ầ,ẩ
b,B
c,C
D,d
đ,Đ
Ẹ,ẹ,É,é,Ẽ,ẽ,Ẻ,ẻ,È,è,E,e
Ễ,ế,Ế,ệ,Ệ,ễ,Ể,ể,Ề,ề,Ê,ê
f,F
G,g
h,H
Ị,ị,Í,í,Ĩ,ĩ,Ỉ,ỉ,Ì,ì,I,i
J,j
k,K
l,L
M,m
n,N
Ọ,Ợ,ợ,Ớ,ớ,Ỡ,ỡ,Ở,ọ,Ó,ó,o,O,ò,Ò,ỏ,Ỏ,õ,Õ
Ộ,ộ,Ố,ố,ô,Ô,ồ,Ồ,ổ,Ổ,ỗ,Ỗ
ở,Ờ,ờ,Ơ,ơ
P,p
q,Q
r,R
S,s
t,T
Ư,ừ,Ừ,ử,Ử,ữ,Ữ,ứ,Ứ,ự,Ự,ư,Ụ,u,U,ù,Ù,ủ,Ủ,ũ,Ũ,ú,Ú,ụ
V,v
w,W
X,x
Ỵ,ỵ,Ý,ý,Ỹ,ỹ,Ỷ,ỷ,Ỳ,ỳ,Y,y
z,Z