Clickthrough for active ads

You’re given the following tables, showing information for individual advertising campaigns as well as associated clicks, impressions.

Table: ads

ad_id	status
1234	Active
1235	Active
1236	Inactive
4454	Active
4432	Inactive
4430	Active
1299	Active

Table: ad_events

event_id	ad_id	event_type	count
115	1234	Click	500
116	1235	Impression	5000
117	1236	Click	200
118	4454	Impression	6500
119	4432	Click	50
120	4430	Impression	10000
121	1299	Click	150
122	1234	Impression	12000
123	1235	Click	75
124	1236	Impression	2000
125	4454	Click	65
126	4432	Impression	5500
127	4430	Click	100
128	1299	Impression	15000

Given the tables above, write a SQL query to return the clickthrough rate (number of clicks / number of impressions) for all active ads.

You can view/query the data in an interactive SQL fiddle here.