Return data type of aggregate function

Good day,
I am working on converting windows applications, so it can be used with SQL server and Informix database. In a SQL server, the return data type of the SUM () function is the same as the data type of the column begin summed. So, if I sum integer field I get integer data type. It appears in Informix, that no matter what I SUM (), I get a float data type.
I have two questions:
1-Is there a setting that could change this?
2-What other aggregate functions does this apply to?
Thank you in advance for your help.
Regards.
