Time-to-Conversion SQL by Channel | Dataford Interview Questions

Your question is Time-to-Conversion SQL by Channel. Start with the requirements and the two tables on the right.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

Aircall's marketing team wants to compare how quickly leads from LinkedIn and Google Ads convert. Assume the query runs on 2026-08-29, and define the six-month period as the interval beginning six months before the run date.

Write a PostgreSQL query that calculates the average time from lead creation to conversion for each requested source.

Requirements

Include only leads created within the last six months whose source is LinkedIn or Google Ads.
Join leads to their conversion records and calculate elapsed time in days using timestamps.
Return one row per source, with the average rounded to two decimal places. Leads without a conversion must not contribute to the average.
Order the output alphabetically by source.

Schema

leads

Column	Type	Description
lead_idPK	BIGINT	Unique lead identifier
source	VARCHAR(50)	Marketing acquisition source
created_at	TIMESTAMP	Timestamp when the lead entered the marketing funnel

conversions

Column	Type	Description
conversion_idPK	BIGINT	Unique conversion record identifier
lead_id	BIGINT	Lead associated with the conversion
converted_at	TIMESTAMP	Timestamp when the lead converted