hard20 pts · first answer countssqlmetrics

Click-through rate with zero impressions

Some ads have 0 impressions. Which expression computes click-through rate without an error and without hiding the problem as a fake 0%?

A.clicks / impressionsB.clicks / (impressions + 1)C.COALESCE(clicks / impressions, 0)D.clicks * 1.0 / NULLIF(impressions, 0)