Direct query resulting in infinity calculation

I'm using a direct query of a redshift data source and I'm having two issues.

1. A calculation is sometimes but not always calculating incorrectly and showing an output of infinity, you can see on the table below, particularly on the Paid search CTR that the rows around the highlighted one are calculating correctly but for that row (and a number of others not shown it is resulting in an infinity result).  The calculation for ROAS is sum(sum_ga_transaction_revenue)/sum(sum_cost) and the calculation for CTR is sum(sum_clicks)/sum(sum_impressions).

2. The underlying data has values with decimal points but when it is summed as in the table below it is rounding off the values.

Any help would be appreciated!