Run different SQL statements using If Then with a variable

Trying to do something very simple. Using If/Then, is there a way to run a separate Select statement based on the value of a variable? The function GetTotalActiveUnits() in the below code returns an integer.

    set @RetVal =  GetTotalActiveUnits(CustomerCode);
    if  @RetVal = 0 then 
    Select * from tblREF_UnitInfo;
    else
    select * from tblREF_State;
    end if

There is no problem with your code - at least as far as IF is concerned and if it is in a stored routine.

drop procedure if exists p;
delimiter $$
create procedure p(inp int)
begin
     set @RetVal = inp;# GetTotalActiveUnits(CustomerCode);
    if  @RetVal = 0 then 
     select @retval ;
    else
     select @retval ;
    end if ;

end $$

delimiter ;

call p(1);
+---------+
| @retval |
+---------+
|       1 |
+---------+
1 row in set (0.001 sec)

call p(0)
+---------+
| @retval |
+---------+
|       0 |
+---------+
1 row in set (0.001 sec)