Fix numeric compare in SQL

[mvorisek]

fixes #950, especially SUM(1) = bind<1.0>

see https://dba.stackexchange.com/questions/311555/sqlite-spec-4-2-type-conversions-prior-to-comparison

the actual issue is: http://sqlfiddle.com/#!5/e9c19/9 (datype cannot be determined before the query is run, as the INTEGER/REAL datatype might be not large enough to represent the aggregated number)