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First and Last Interaction with CTEs
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First and Last Interaction with CTEs

MediumSQL · PostgreSQL

Problem

Given a table of event logs, identify the first and last interaction for each user using common table expressions.

Use occurred_at to determine chronological order. Ignore rows where occurred_at is NULL. If a user has multiple events at the same timestamp, use the smallest interaction_id as the first event and the largest as the last event.

Output

  1. One row per user with at least one timestamped interaction.
  2. Columns: user_id, first_interaction_at, first_event_type, last_interaction_at, last_event_type.
  3. Order by user_id ascending.

Schema

event_logs
ColumnTypeDescription
interaction_idPKINTUnique identifier for the interaction
user_idINTIdentifier of the user who generated the event
occurred_atTIMESTAMPTZTimestamp when the interaction occurred
event_typeVARCHAR(40)Type of user interaction
surfaceVARCHAR(40)Product surface where the event occurred
Tablesevent_logs
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