CREATE MATERIALIZED VIEW openmeter.om_default_tokens_total
(

    ...

    `model` String,  -- GroupBy1
    `type` String    -- GroupBy2
)
...
AS SELECT
    ...
    JSON_VALUE(data,
 '$.model') AS model,

    JSON_VALUE(data,
 '$.type') AS type
    ...

ALTER TABLE
  openmeter.om_events
ADD
  PROJECTION om_default_api_requests_total (
    SELECT
      -- Further pre-calculted fields can be added here to speed up execution, e.g. (empty(openmeter.om_events.validation_error) = 1)...
      subject,
      tumbleStart(
        time,
        toIntervalMinute(1)
      ) AS windowstart,
      tumbleEnd(
        time,
        toIntervalMinute(1)
      ) AS windowend,
      sumState(
        cast(
          JSON_VALUE(data, '$.tokens'),
          'Float64'
        )
      ) AS value,
      JSON_VALUE(data, '$.model') as model,
      JSON_VALUE(data, '$.type') as type
    /**
      * Note the missing WHERE block compared to the MATERIALIZED VIEW.
      * Where blocks are not currently supported in PROJECTIONs, with their priority on the roadmap being questionable:
      * https://github.com/ClickHouse/ClickHouse/issues/33678
      *
      * This is not necessaraly an issue as the filtering can take place in the actual query (planner still using the PROJECTION for a limited set of results), but it in itself would warrant some modifications:
      * - Meters wouldn't phisically be separate on the DB level. Meters of different namespaces would use the same underlying projections so additonal caution would be needed.
      * - The projections would be populated with a lot of nonsensical data. e.g: in the example above most of the events wouldn't have a `$.model` field. Clickhouse doesn't complain about per say right now but if the group by functionality would be extended in the future it could cause issues.
     */
    GROUP BY
      windowstart,
      windowend,
      subject,
      model,
      type
  );

-- Simple way of forcing projeciton to be used by mirroring it's SELECT block
WITH proj AS (
  subject,
      tumbleStart(
        time,
        toIntervalMinute(1)
      ) AS windowstart,
      tumbleEnd(
        time,
        toIntervalMinute(1)
      ) AS windowend,
      sumState(
        cast(
          JSON_VALUE(data, '$.tokens'),
          'Float64'
        )
      ) AS value,
      JSON_VALUE(data, '$.model') as model, -- Note how we need to reference the JSONPath here
      JSON_VALUE(data, '$.type') as type -- And here
  FROM
    openmeter.om_events
  -- Note re-introducing the WHERE block. This does not affect the query planning, it still uses the projection.
  WHERE
    (openmeter.om_events.namespace = 'default')
    AND (empty(openmeter.om_events.validation_error) = 1)
    AND (openmeter.om_events.type = 'prompt')
  GROUP BY
    windowstart,
    windowend,
    subject,
    model,
    type
) SELECT windowstart, windowend, sumMerge(value) AS value, subject, model, type
FROM proj
WHERE
  (subject = ?)
  AND windowstart >= ?
  AND windowend <= ?
GROUP BY
  windowstart,
  windowend,
  subject,
  group1,
  group2
ORDER BY
  windowstart