assess the xlread in elsefi command

xlread is used to read xls files i want to use this command in ifelse condiations

if input==a
  B=AS
elseif 
  B=AQ

 it means that xlread the column AS
how i generate the code for above algorithm 

columnB = xlsread(filename,'B:B')

[EDITED, Jan, please format the code properly, thanks]

Answer 1

[Jan]

if strcmp(in, 'a')
  B = 'AS';
else  % not elseif
  B = 'AQ';
end
columnB = xlsread(filename, [B, ':', B]);