run: events -> {
    where: trim(event_name) = "purchase"
    select: event_date
    select: event_name
    calculate: prev_occur is lag(event_date) {
        partition_by: event_name
        order_by: event_date asc
    }
    order_by: event_name asc, event_date asc
}

run: order_items -> {
    select: 
      user_id
      created_at

    calculate: prev_occur is lag(created_at) {
        partition_by: user_id
        order_by: created_at asc
    }
    order_by: user_id asc, created_at asc
}

run: events -> {
    where: trim(event_name) = "purchase"
    select: event_date
    select: event_name
    calculate: prev_occur is lag(event_date) {
        partition_by: event_name
        order_by: event_date asc
    }
    order_by: event_name asc, event_date asc
}