Compute Avg Days to First Reaction | Dataford Interview Questions

Your question is Compute Avg Days to First Reaction. Start with the requirements and the two tables on the right.

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Problem

Meta wants to measure how quickly people react after starting a conversation in Messenger. Write a SQL query to calculate the average number of days from each conversation's start time to the first reaction used in that conversation.

Requirements

Use the conversations table to get each conversation start time.
Use the message_reactions table to find the first reaction timestamp per conversation.
Return only conversations that have at least one reaction.
Output the average delay in days across all qualifying conversations, rounded to 2 decimal places.

Schema

conversations

Column	Type	Description
conversation_idPK	BIGINT	Primary key for the conversation thread
thread_type	VARCHAR(20)	Surface type such as dm, group, or fb_groups
started_at	TIMESTAMP	Timestamp when the conversation started

message_reactions

Column	Type	Description
reaction_idPK	BIGINT	Primary key for the reaction event
conversation_id	BIGINT	Foreign key to conversations.conversation_id
reacted_at	TIMESTAMP	Timestamp when the reaction was used
reaction_type	VARCHAR(20)	Reaction type such as like, love, haha, wow, care, or sad