SQLite Forum

How to convert the data type of the new column in the view?
If you mean that you want the affinity of test1111.fp2 to be real then you can declare the view as:

CREATE VIEW test1111 
          cast(SUM(future_price) as REAL) as fp2
     FROM t_spotprice
    WHERE tradingday = 20200103;

The affinity of the result of an expression (which also includes functions) is NONE (No Affinity).  This is quite separate from the datatype of the result value.