GA4 Multi-Step, Multi-Cycle Marketing Attribution example using the BigQuery GA4 Sample Dataset at https://developers.google.com/analytics/bigquery/web-ecommerce-demo-dataset

ga4_attribution.sql

WITH
  events AS (
  SELECT
    TIMESTAMP_MICROS(event_timestamp) AS event_ts,
    CONCAT(user_pseudo_id,'-',event_name,'-',CAST(event_timestamp AS STRING)) AS event_id,
    user_pseudo_id AS user_pseudo_id,
    user_id,
    traffic_source.name AS utm_channel,
    traffic_source.medium AS utm_medium,
    traffic_source.source AS utm_source,
    event_name AS event_type,
    (
    SELECT
      value.int_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'ga_session_id') AS session_id,
    (
    SELECT
      value.int_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'ga_session_number') AS session_number,
    (
    SELECT
      value.string_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'page_referrer') AS referrer_host,
    (
    SELECT
      value.string_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'page_location') AS page_path,
    (
    SELECT
      value.string_value
    FROM
      UNNEST(event_params)
    WHERE
      event_name = 'page_view'
      AND KEY = 'page_title') AS page_title,
    ecommerce.purchase_revenue AS order_value,
    ecommerce.transaction_id AS order_id,
    platform AS channel,
    device.category AS device_category,
    device.operating_system,
    device.language,
    device.is_limited_ad_tracking,
    NULL AS browser,
    NULL AS hostname,
    geo.continent,
    geo.country,
    geo.region,
    geo.city
  FROM
    `bigquery-public-data.ga4_obfuscated_sample_ecommerce.events_*` -- modify to your project
    ),
  id_stitching AS (
  SELECT
    DISTINCT user_pseudo_id AS user_pseudo_id,
    LAST_VALUE(user_id IGNORE NULLS) OVER (PARTITION BY user_pseudo_id ORDER BY event_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING ) AS user_id,
    MIN(event_ts) OVER (PARTITION BY user_pseudo_id ) AS first_seen_at,
    MAX(event_ts) OVER (PARTITION BY user_pseudo_id ) AS last_seen_at
  FROM
    events),
  sessions AS (
  SELECT
    user_pseudo_id,
    TIMESTAMP_MICROS(event_timestamp) AS session_start_ts,
    CAST(LEAD(TIMESTAMP_MICROS(event_timestamp),1) OVER (PARTITION BY CONCAT(user_pseudo_id)
      ORDER BY
        event_timestamp) AS timestamp) AS session_end_ts,
    (
    SELECT
      value.int_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'ga_session_id') AS session_id,
    (
    SELECT
      value.int_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'ga_session_number') AS session_number,
    (
    SELECT
      value.string_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'page_referrer') AS referrer_host,
    (
    SELECT
      value.string_value
    FROM
      UNNEST(event_params)
    WHERE
      KEY = 'page_location') AS landing_page_path,
    (
    SELECT
      value.string_value
    FROM
      UNNEST(event_params)
    WHERE
      event_name = 'page_view'
      AND KEY = 'page_title') AS landing_page_title,
    traffic_source.name AS utm_campaign,
    traffic_source.medium AS utm_medium,
    traffic_source.source AS utm_source,
    platform AS channel,
    CASE
      WHEN device.category = "desktop" THEN "desktop"
      WHEN device.category = "tablet"
    AND app_info.id IS NULL THEN "tablet-web"
      WHEN device.category = "mobile" AND app_info.id IS NULL THEN "mobile-web"
      WHEN device.category = "tablet"
    AND app_info.id IS NOT NULL THEN "tablet-app"
      WHEN device.category = "mobile" AND app_info.id IS NOT NULL THEN "mobile-app"
  END
    AS device,
    device.mobile_brand_name mobile_brand_name,
    device.mobile_model_name mobile_model_name,
    device.mobile_marketing_name mobile_marketing_name,
    device.mobile_os_hardware_model mobile_os_hardware_model,
    device.operating_system operating_system,
    device.operating_system_version operating_system_version,
    device.vendor_id vendor_id,
    device.advertising_id advertising_id,
    device.language LANGUAGE,
    device.is_limited_ad_tracking is_limited_ad_tracking,
    device.time_zone_offset_seconds,
    NULL AS browser,
    NULL AS browser_version,
    NULL AS browser,
    device.web_info.browser_version,
    NULL AS hostname,
    geo.continent continent,
    geo.country country,
    geo.region region,
    geo.city city,
    COUNT(DISTINCT CONCAT(user_pseudo_id,'-',event_name,'-',CAST(event_timestamp AS STRING))) OVER (PARTITION BY (SELECT value.int_value FROM UNNEST(event_params)
      WHERE
        KEY = 'ga_session_id')) AS events
  FROM
    `bigquery-public-data.ga4_obfuscated_sample_ecommerce.events_*` s -- modify to your project
  WHERE
    event_name = 'session_start' ),
  user_stitched_sessions AS (
  SELECT
    sessions.*,
    COALESCE(id_stitching.user_id, sessions.user_pseudo_id) AS blended_user_id
  FROM
    sessions
  LEFT JOIN
    id_stitching
  USING
    (user_pseudo_id) ),
  user_stitched_events AS (
  SELECT
    events.*,
    COALESCE(id_stitching.user_id, events.user_pseudo_id) AS blended_user_id
  FROM
    events
  LEFT JOIN
    id_stitching
  USING
    (user_pseudo_id) ),
  events_filtered AS (
  SELECT
    *
  FROM (
    SELECT
      *,
      FIRST_VALUE(CASE
          WHEN event_type = 'add_payment_info' THEN event_id
      END
        IGNORE NULLS) OVER (PARTITION BY blended_user_id ORDER BY event_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS first_registration_event_id,
      FIRST_VALUE(CASE
          WHEN event_type='purchase' THEN event_id
      END
        IGNORE NULLS) OVER (PARTITION BY blended_user_id ORDER BY event_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING ) AS first_order_event_id
    FROM
      user_stitched_events )
  WHERE
    event_type = 'purchase'
    OR (event_type='add_payment_info'
      AND event_id = first_registration_event_id) ),
  converting_events AS (
  SELECT
    e.blended_user_id,
    session_id,
    event_type,
    order_id AS order_id,
    CASE
      WHEN event_type='purchase' AND event_id = first_order_event_id THEN order_value
    ELSE
    0
  END
    AS first_order_revenue,
    CASE
      WHEN event_type='purchase' AND event_id != first_order_event_id THEN order_value
    ELSE
    0
  END
    AS repeat_order_revenue,
    CASE
      WHEN event_type IN ('purchase' ) THEN 1
    ELSE
    0
  END
    AS count_conversions,
    CASE
      WHEN event_type='purchase' AND event_id = first_order_event_id THEN 1
    ELSE
    0
  END
    AS count_first_order_conversions,
    CASE
      WHEN event_type='purchase' AND event_id != first_order_event_id THEN 1
    ELSE
    0
  END
    AS count_repeat_order_conversions,
    CASE
      WHEN event_type = 'purchase' THEN 1
    ELSE
    0
  END
    AS count_order_conversions,
    CASE
      WHEN event_type='add_payment_info' AND event_id = first_registration_event_id THEN 1
    ELSE
    0
  END
    AS count_registration_conversions,
    event_ts AS converted_ts
  FROM
    events_filtered e ),
  converting_sessions_deduped AS (
  SELECT
    session_id AS session_id,
    MAX(blended_user_id) AS blended_user_id,
    /* note that because a session could in-theory contain account opening, first order and multiple repeat order events (conversions) within the same session, we have to aggregate the value of those conversions when working at the session level */ 
    SUM(first_order_revenue) AS first_order_revenue,
    SUM(repeat_order_revenue) AS repeat_order_revenue,
    SUM(count_first_order_conversions) AS count_first_order_conversions,
    SUM(count_repeat_order_conversions) AS count_repeat_order_conversions,
    SUM(count_order_conversions) AS count_order_conversions,
    SUM(count_registration_conversions) AS count_registration_conversions,
    SUM(count_registration_conversions) + SUM(count_first_order_conversions) + SUM(count_repeat_order_conversions) AS count_conversions,
    MAX(converted_ts) AS converted_ts,
    MIN(converted_ts) AS min_converted_ts
  FROM
    converting_events
  GROUP BY
    1 ),
  /* Combine (join) those conversion sessions with all of the sessions that led-up to those conversions */ 
  touchpoint_and_converting_sessions_labelled AS (
  SELECT
    *
  FROM (
    SELECT
      *,
      FIRST_VALUE(converted_ts IGNORE NULLS) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS conversion_cycle_conversion_ts,
      -- used later on to calculate days to conversion
      ROW_NUMBER() OVER (PARTITION BY blended_user_id ORDER BY session_start_ts) AS session_seq
    FROM (
      SELECT
        s.blended_user_id AS blended_user_id,
        s.session_id AS session_id,
        s.session_start_ts AS session_start_ts,
        s.session_end_ts AS session_end_ts,
        c.converted_ts AS converted_ts,
        c.min_converted_ts AS min_converted_ts,
        COALESCE(SUM(c.count_conversions),0) AS count_conversions,
        COALESCE(SUM(c.count_order_conversions),0) AS count_order_conversions,
        COALESCE(SUM(c.count_first_order_conversions),0) AS count_first_order_conversions,
        COALESCE(SUM(c.count_repeat_order_conversions),0) AS count_repeat_order_conversions,
        COALESCE(SUM(c.count_registration_conversions),0) AS count_registration_conversions,
        COALESCE(CASE
            WHEN c.count_conversions >0 THEN TRUE
          ELSE
          FALSE
        END
          ,FALSE) AS conversion_session,
        COALESCE(CASE
            WHEN c.count_conversions >0 THEN 1
          ELSE
          0
        END
          ,0) AS conversion_event,
        --used when calculating the conversion cycle number
        COALESCE(CASE
            WHEN c.count_order_conversions>0 THEN 1
          ELSE
          0
        END
          ,0) AS order_conversion_event,
        --used when calculating the order converion cycle number
        COALESCE(CASE
            WHEN c.count_registration_conversions>0 THEN 1
          ELSE
          0
        END
          ,0) AS registration_conversion_event,
        -- see above
        COALESCE(CASE
            WHEN c.count_first_order_conversions>0 THEN 1
          ELSE
          0
        END
          ,0) AS first_order_conversion_event,
        -- ditto
        COALESCE(CASE
            WHEN c.count_repeat_order_conversions>0 THEN 1
          ELSE
          0
        END
          ,0) AS repeat_order_conversion_event,
        -- ditto
        utm_source AS utm_source,
        CAST(NULL AS string) AS utm_content,
        utm_medium AS utm_medium,
        utm_campaign AS utm_campaign,
        referrer_host AS referrer_host,
        channel AS channel,
        CASE
          WHEN LOWER(utm_source) IN ('(direct)', '(data deleted)', '<other>') THEN FALSE
        ELSE
        TRUE
      END
        AS is_non_direct_channel,
        CASE
          WHEN LOWER(utm_medium) LIKE '%paid%' THEN TRUE
        ELSE
        FALSE
      END
        AS is_paid_channel,
        events AS events,
        c.first_order_revenue,
        c.repeat_order_revenue,
        city,
        continent,
        country,
        region
      FROM
        user_stitched_sessions s
      LEFT JOIN
        converting_sessions_deduped c
      ON
        s.session_id = c.session_id
      GROUP BY
        1,
        2,
        3,
        4,
        5,
        6,
        12,
        13,
        14,
        15,
        16,
        17,
        18,
        19,
        20,
        21,
        22,
        23,
        24,
        25,
        26,
        27,
        28,
        29,
        30,
        31,
        32) )
  WHERE
    conversion_cycle_conversion_ts >= session_start_ts ),

  /* This is a multi-cycle attribution model which means that we attribute the value of each order placed by a user to the sessions that led to that order, starting with the session after the last order
      We therefore need to split each users' sessions into "conversion cycles", the sessions leading-up to and potentially including the session in which the conversion happened. This next CTE starts this
      process of calculating those conversion cycles by first calculating, for each session for each user, how many conversions of each type have been recorded for that user at the time the session started
      by summing the number of conversions recorded in the rows (sessions) up to and including the current row (session) */ 
      
  touchpoint_and_converting_sessions_labelled_with_conversion_number AS (
  SELECT
    *,
    SUM(conversion_event) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) AS user_total_conversions,
    SUM(count_order_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) AS user_total_order_conversions,
    SUM(count_registration_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) AS user_total_registration_conversions,
    SUM(count_first_order_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) AS user_total_first_order_conversions,
    SUM(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) AS user_total_repeat_order_conversions
  FROM
    touchpoint_and_converting_sessions_labelled ),
    
    /* A conversion cycle is defined as all sessions (rows) leading up-to and including the conversion session (conversion cycle #1), with the conversion cycle then incrementing to conversion cycle #2 for the rows leading up to the next conversion, then we're on to conversion cycle #3, and so on.
      There can only be one conversion cycle for user registration conversions, and the same is true for first order conversions. Repeat order conversions start at conversion cycle #1 (if the user has made their second order) and then increment to #2 for the users' third order, etc. This block of code calculates which conversion cycle each row (session) is within for each of the conversion cycle types */ 
      
  touchpoint_and_converting_sessions_labelled_with_conversion_number_and_conversion_cycles AS (
  SELECT
    *,
    CASE
      WHEN registration_conversion_event = 0 THEN MAX(COALESCE(user_total_registration_conversions,0)) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) + 1
    ELSE
    MAX(user_total_registration_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW )
  END
    AS user_registration_conversion_cycle,
    CASE
      WHEN conversion_event = 0 THEN MAX(COALESCE(user_total_conversions,0)) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) + 1
    ELSE
    MAX(user_total_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW )
  END
    AS user_conversion_cycle,
    CASE
      WHEN first_order_conversion_event = 0 THEN MAX(COALESCE(user_total_first_order_conversions,0)) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) + 1
    ELSE
    MAX(user_total_first_order_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW )
  END
    AS user_first_order_conversion_cycle,
    CASE
      WHEN repeat_order_conversion_event = 0 THEN MAX(COALESCE(user_total_repeat_order_conversions,0)) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) + 1
    ELSE
    MAX(user_total_repeat_order_conversions) OVER (PARTITION BY blended_user_id ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW )
  END
    AS user_repeat_order_conversion_cycle
  FROM
    touchpoint_and_converting_sessions_labelled_with_conversion_number ),

  /* As we only consider rows (sessions) within a certain number of days before each conversion happened (the "lookback window") we first have to calculate a day number for each row.
      We do this by reference to a set starting date, arbitrarily chosen (2018-01-01) with the assumption that it's earlier than any conversion we need to attribute value for;
      we could also achieve the same result (turning date into a number) via the Unix date or a similar date>integer transformation */ 
      
  touchpoint_and_converting_sessions_labelled_with_conversion_number_and_conversion_cycles_and_day_number AS (
  SELECT
    *,
    (DATE_DIFF(DATE(session_start_ts),DATE('2018-01-01'),DAY)) AS session_day_number
  FROM
    touchpoint_and_converting_sessions_labelled_with_conversion_number_and_conversion_cycles ),
  
  /* now we calculate how many days before the next conversion each row (session) is,
      and then determine, based on a variable set in the dbt_project.yml file, whether the row (session) is within
      the regular attribution, and time decay attribution, look-back windows */ 
  
  days_to_each_conversion AS (
    SELECT
    *,
    MAX(session_day_number) OVER (PARTITION BY blended_user_id, user_conversion_cycle) - session_day_number AS days_before_conversion,
    (MAX(session_day_number) OVER (PARTITION BY blended_user_id, user_conversion_cycle) - session_day_number )<= 30 AS is_within_attribution_lookback_window,
    (MAX(session_day_number) OVER (PARTITION BY blended_user_id, user_conversion_cycle) - session_day_number ) <= 7 AS is_within_attribution_time_decay_days_window
  FROM
    touchpoint_and_converting_sessions_labelled_with_conversion_number_and_conversion_cycles_and_day_number ),
  /* Time-decay attribution is a multi-touch attribution model that gives some credit to all the channels that led to your customer converting,
      with that amount of credit being less (decaying) the further back in time the channel was interacted with.
      This CTE calculates the various numbers we need as inputs to the time decay calculation */ 
  
  add_time_decay_score AS (
  SELECT
    *,
  IF
    (is_within_attribution_time_decay_days_window, POW(2,days_before_conversion-1)/NULLIF(7,0),NULL) AS time_decay_score,
  IF
    (conversion_session,1,POW(2, (days_before_conversion - 1))) AS weighting,
  IF
    (conversion_session,1,(COUNT(CASE
            WHEN NOT conversion_session OR TRUE THEN session_id
        END
          ) OVER (PARTITION BY blended_user_id, DATE_TRUNC(CAST(session_start_ts AS date),DAY)))) AS sessions_within_day_to_conversion,
  IF
    (conversion_session,1,safe_divide (POW(2, (days_before_conversion - 1)),
        COUNT(CASE
            WHEN NOT conversion_session OR TRUE THEN session_id
        END
          ) OVER (PARTITION BY blended_user_id, DATE_TRUNC(CAST(session_start_ts AS date),DAY)))) AS weighting_split_by_days_sessions
  FROM
    days_to_each_conversion ),

  /* Because time-decay attribution adjusts the attributed value of the conversion by looking at the DAYS before the conversion happened and not the rows (sessions) before the conversion,
      the time decay attribution score calculated in the CTE above will end-up assigning the value of that days attributed conversions to all of the rows (sessions) recorded for that day,
      of which there may well be more than one for each day. So we then split the value of that day's conversion across the sessions within that day, equally, so we don't end-up over-counting time decay conversions */ 
      split_time_decay_score_across_days_sessions AS (
  SELECT
    *,
    time_decay_score/NULLIF(sessions_within_day_to_conversion,0) AS apportioned_time_decay_score
  FROM
    add_time_decay_score ),

  /* Calculate the first/last non-direct/paid sessions in each conversion cycle
      and all conversion cycles that include non-direct and paid channel sessions.
      These flags are used in the actual session attribution calculations in the next CTE */ /* "and not True" excludes the session from any attribution of the conversion.
      Option is set via the "attribution_include_conversion_session: true" variable definition in the dbt_project.yml config file.
      Default value of "true" has the effect of including the actual session that the conversion happened in within the set of sessions eligable for attribution.
      Reason for including this option is because for sessions generated by dbt (for the custom transactions and account openings that couldn't be linked to a session)
      you might want to exclude these from having conversions all or partly attributed to them as they couldn't possibly have marketing channel information recorded for them.
      However the option to exclude them (setting this variable to "false") has not been enabled, so they are included in-scope for attribution (unless subsequently it's set to "false")  */ 
      
  attrib_calc_flags AS (
  SELECT
    *,
  IF
    (FIRST_VALUE(CASE
          WHEN is_within_attribution_lookback_window AND is_non_direct_channel = TRUE THEN session_id
      END
        IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) = session_id,TRUE,FALSE) AS is_first_non_direct_channel_in_conversion_cycle,
  IF
    (LAST_VALUE(CASE
          WHEN is_within_attribution_lookback_window AND is_non_direct_channel = TRUE THEN session_id
      END
        IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)=session_id,TRUE,FALSE) AS is_last_non_direct_channel_in_conversion_cycle,
  IF
    (SUM(CASE
          WHEN is_within_attribution_lookback_window AND is_non_direct_channel = TRUE THEN 1
      END
        ) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)>0,TRUE,FALSE) AS is_conversion_cycle_with_non_direct,
  IF
    (FIRST_VALUE(CASE
          WHEN is_within_attribution_lookback_window AND is_paid_channel = TRUE THEN session_id
      END
        IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)=session_id,TRUE,FALSE) AS is_first_paid_channel_in_conversion_cycle,
  IF
    (LAST_VALUE(CASE
          WHEN is_within_attribution_lookback_window AND is_paid_channel = TRUE THEN session_id
      END
        IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)=session_id,TRUE,FALSE) AS is_last_paid_channel_in_conversion_cycle,
  IF
    (SUM(CASE
          WHEN is_within_attribution_lookback_window AND is_paid_channel = TRUE THEN 1
      END
        ) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)>0,TRUE,FALSE) AS is_conversion_cycle_with_paid
  FROM
    split_time_decay_score_across_days_sessions ),
  session_attrib_pct AS (
  SELECT
    *,
  IF
    (conversion_session
      AND NOT TRUE,0,
      CASE
        WHEN session_id = LAST_VALUE( IF (is_within_attribution_lookback_window,session_id,NULL) IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) THEN 1
      ELSE
      0
    END
      ) AS last_click_attrib_pct,
  IF
    (conversion_session
      AND NOT TRUE,0,
      CASE
        WHEN is_last_non_direct_channel_in_conversion_cycle THEN 1 -- if the session is the last qualifying session in the conversion cycle, i.e. last non-direct session, then allocate 100% of conversion to it
        WHEN
    IF
      (NOT is_conversion_cycle_with_non_direct
        AND session_id = LAST_VALUE(
        IF
          (is_within_attribution_lookback_window,session_id,NULL) IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),TRUE,FALSE) = TRUE THEN 1 -- else if there are no non-direct channel sessions in the conversion cycle AND this the last session in that conversion cycle, allocate 100% of the conversion to it
      ELSE
      0 -- else allocate 0%
    END
      ) AS last_non_direct_click_attrib_pct,
  IF
    (conversion_session
      AND NOT TRUE,0,
      CASE
        WHEN is_last_paid_channel_in_conversion_cycle THEN 1 -- if the session is the last qualifying session in the conversion cycle, i.e. last paid session, then allocate 100% of conversion to it
        WHEN
    IF
      (NOT is_conversion_cycle_with_paid
        AND session_id = LAST_VALUE(
        IF
          (is_within_attribution_lookback_window,session_id,NULL) IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),TRUE,FALSE) = TRUE THEN 1 -- else if there are no paid channel sessions in the conversion cycle AND this the last session in that conversion cycle, allocate 100% of the conversion to it
      ELSE
      0 -- else allocate 0%
    END
      ) AS last_paid_click_attrib_pct,
  IF
    (conversion_session
      AND NOT TRUE,0,
      CASE
        WHEN session_id = FIRST_VALUE( IF (is_within_attribution_lookback_window,session_id,NULL) IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) THEN 1
      ELSE
      0
    END
      ) AS first_click_attrib_pct,
  IF
    (conversion_session
      AND NOT TRUE,0,
      CASE
        WHEN is_first_non_direct_channel_in_conversion_cycle THEN 1 -- if the session is the first qualifying session in the conversion cycle, i.e. first non-direct session, then allocate 100% of conversion to it
        WHEN
    IF
      (NOT is_conversion_cycle_with_non_direct
        AND session_id = FIRST_VALUE(
        IF
          (is_within_attribution_lookback_window,session_id,NULL) IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),TRUE,FALSE) = TRUE THEN 1 -- else if there are no non-direct channel sessions in the conversion cycle AND this the first session in that conversion cycle, allocate 100% of the conversion to it
      ELSE
      0 -- else allocate 0%
    END
      ) AS first_non_direct_click_attrib_pct,
  IF
    (conversion_session
      AND NOT TRUE,0,
      CASE
        WHEN is_first_paid_channel_in_conversion_cycle THEN 1 -- if the session is the first qualifying session in the conversion cycle, i.e. first paid session, then allocate 100% of conversion to it
        WHEN
    IF
      (NOT is_conversion_cycle_with_paid
        AND session_id = FIRST_VALUE(
        IF
          (is_within_attribution_lookback_window,session_id,NULL) IGNORE NULLS) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),TRUE,FALSE) = TRUE THEN 1 -- else if there are no paid channel sessions in the conversion cycle AND this the first session in that conversion cycle, allocate 100% of the conversion to it
      ELSE
      0 -- else allocate 0%
    END
      ) AS first_paid_click_attrib_pct,
  IF
    (conversion_session
      AND NOT TRUE,0,
    IF
      (is_within_attribution_lookback_window,(safe_divide (1,
            (COUNT(
              IF
                (is_within_attribution_lookback_window,session_id,NULL)) OVER (PARTITION BY blended_user_id, user_conversion_cycle ORDER BY session_start_ts ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) + 0))),0) ) AS even_click_attrib_pct,
  IF
    (conversion_session
      AND NOT TRUE,0,CASE
        WHEN is_within_attribution_time_decay_days_window THEN apportioned_time_decay_score / NULLIF((SUM(apportioned_time_decay_score) OVER (PARTITION BY blended_user_id, user_conversion_cycle)),0)
    END
      ) AS time_decay_attrib_pct
  FROM
    attrib_calc_flags ),
  
  /* Now calculate the actual account opening, first order, repeat order and revenue numbers based on the attribution percentages calculated for the session */ 
  /* Max() aggregations are used to find the conversion value that each session-level percentage attribution is then applied to */ 
  
  final AS (
  SELECT
    'Last Click' AS MODEL,
    (MAX(count_registration_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_click_attrib_pct) AS user_registration_conversions,
    (MAX(count_first_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_click_attrib_pct) AS first_order_conversions,
    (MAX(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_click_attrib_pct) AS repeat_order_conversions,
    (MAX(first_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_click_attrib_pct) AS first_order_revenue,
    (MAX(repeat_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_click_attrib_pct) AS repeat_order_revenue,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    conversion_session AS is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region
  FROM
    session_attrib_pct a
  UNION ALL
  SELECT
    'First Click' AS MODEL,
    (MAX(count_registration_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_click_attrib_pct) AS user_registration_conversions,
    (MAX(count_first_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_click_attrib_pct) AS first_order_conversions,
    (MAX(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_click_attrib_pct) AS repeat_order_conversions,
    (MAX(first_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_click_attrib_pct) AS first_order_revenue,
    (MAX(repeat_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_click_attrib_pct) AS repeat_order_revenue,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    conversion_session AS is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region
  FROM
    session_attrib_pct a
  UNION ALL
  SELECT
    'Last Non-Direct Click' AS MODEL,
    (MAX(count_registration_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_non_direct_click_attrib_pct) AS user_registration_conversions,
    (MAX(count_first_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_non_direct_click_attrib_pct) AS first_order_conversions,
    (MAX(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_non_direct_click_attrib_pct) AS repeat_order_conversions,
    (MAX(first_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_non_direct_click_attrib_pct) AS first_order_revenue,
    (MAX(repeat_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_non_direct_click_attrib_pct) AS repeat_order_revenue,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    conversion_session AS is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region
  FROM
    session_attrib_pct a
  UNION ALL
  SELECT
    'First Paid Click' AS MODEL,
    (MAX(count_registration_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_paid_click_attrib_pct) AS user_registration_conversions,
    (MAX(count_first_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_paid_click_attrib_pct) AS first_order_conversions,
    (MAX(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_paid_click_attrib_pct) AS repeat_order_conversions,
    (MAX(first_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_paid_click_attrib_pct) AS first_order_revenue,
    (MAX(repeat_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* first_paid_click_attrib_pct) AS repeat_order_revenue,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    conversion_session AS is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region
  FROM
    session_attrib_pct a
  UNION ALL
  SELECT
    'Last Paid Click' AS MODEL,
    (MAX(count_registration_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_paid_click_attrib_pct) AS user_registration_conversions,
    (MAX(count_first_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_paid_click_attrib_pct) AS first_order_conversions,
    (MAX(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_paid_click_attrib_pct) AS repeat_order_conversions,
    (MAX(first_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_paid_click_attrib_pct) AS first_order_revenue,
    (MAX(repeat_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* last_paid_click_attrib_pct) AS repeat_order_revenue,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    conversion_session AS is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region
  FROM
    session_attrib_pct a
  UNION ALL
  SELECT
    'Linear' AS MODEL,
    (MAX(count_registration_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* even_click_attrib_pct) AS user_registration_conversions,
    (MAX(count_first_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* even_click_attrib_pct) AS first_order_conversions,
    (MAX(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* even_click_attrib_pct) AS repeat_order_conversions,
    (MAX(first_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* even_click_attrib_pct) AS first_order_revenue,
    (MAX(repeat_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* even_click_attrib_pct) AS repeat_order_revenue,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    conversion_session AS is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region
  FROM
    session_attrib_pct a
  UNION ALL
  SELECT
    'Time Decay' AS MODEL,
    (MAX(count_registration_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* time_decay_attrib_pct) AS user_registration_conversions,
    (MAX(count_first_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* time_decay_attrib_pct) AS first_order_conversions,
    (MAX(count_repeat_order_conversions) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* time_decay_attrib_pct) AS repeat_order_conversions,
    (MAX(first_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* time_decay_attrib_pct) AS first_order_revenue,
    (MAX(repeat_order_revenue) OVER (PARTITION BY blended_user_id, user_conversion_cycle)* time_decay_attrib_pct) AS repeat_order_revenue,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    conversion_session AS is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region
  FROM
    session_attrib_pct a ),
  pivoted AS (
  SELECT
    MODEL,
    blended_user_id,
    session_id,
    session_start_ts,
    session_end_ts,
    session_seq,
    user_conversion_cycle,
    is_first_non_direct_channel_in_conversion_cycle,
    is_last_non_direct_channel_in_conversion_cycle,
    is_conversion_cycle_with_non_direct,
    is_first_paid_channel_in_conversion_cycle,
    is_last_paid_channel_in_conversion_cycle,
    is_conversion_cycle_with_paid,
    is_non_direct_channel,
    is_paid_channel,
    is_conversion_session,
    utm_source,
    utm_medium,
    utm_campaign,
    referrer_host,
    channel,
    city,
    continent,
    country,
    region,
    user_registration_conversions,
    first_order_conversions,
    repeat_order_conversions,
    first_order_revenue,
    repeat_order_revenue
  FROM
    final)
SELECT
  *
FROM
  pivoted

Apparently, I'm wrong with "real" data: GROUP BY on user_pseudo_id, event_name, event_timestamp gives you count(*) > 1

Have You analysed more precisely these cases?

You need these:

(SELECT value.string_value FROM UNNEST(event_params) WHERE key="source") as source,
(SELECT value.string_value FROM UNNEST(event_params) WHERE key="medium") as medium,

Yeah this is event_params UTMs.
What I'm saying is that you have also UTM at record level (traffic_source, traffic_medium, traffic_name) and at page_location level (in url, e.g. &utm_source, &utm_medium). Btw they are not always present in all the three places and actually would like to understand the difference among the three.

as exception there might be case
when you have at least one NULL value (any of user_pseudo_id,event_name,event_timestamp) in your string concatenation:

CONCAT(user_pseudo_id,'-',event_name,'-',CAST(event_timestamp AS STRING)) AS event_id

this will return NULL as result for record

there is proof
check it in your bigquery:

select 1,concat(NULL,'a','b') -- NULL
union all
select 2,concat('a',NULL,'b') -- NULL
union all
select 3,concat('a','b',NULL) -- NULL

so if this not excpected
use

CONCAT( IFNULL(user_pseudo_id,'some')
              ,'-'
              ,IFNULL(event_name,'thing')
              ,'-'
              ,IFNULL(CAST(event_timestamp AS STRING),'happend')
              ) AS event_id