text: -- Increase mime_type field size
  ALTER TABLE oc_assets_asset ALTER COLUMN mime_type TYPE VARCHAR (255);
  
  -- Add modified and deletion date fields to series.
  --
  -- The deletion date is straight forward, as all existing records can correctly use 'null' as value.
  -- Modification date is more tricky. We don't want to make the field nullable, so we have to find a
  -- somewhat useful value. But we also don't want to set all values to the unix epoch as code
  -- could reasonably assume that almost all modification dates of real world series are unique. So
  -- we instead derive the modification dates from the series' events. Unix epoch only for series
  -- without events.
  ALTER TABLE oc_series ADD deletion_date TIMESTAMP NULL;
  ALTER TABLE oc_series ADD modified_date TIMESTAMP NULL;
  UPDATE oc_series
      SET modified_date = (
          SELECT MAX(oc_search.modification_date)
              FROM oc_search
              WHERE oc_search.series_id = oc_series.id
      );
  UPDATE oc_series
      SET modified_date = TIMESTAMP '1970-01-01 00:00:01'
      WHERE modified_date IS NULL;
  ALTER TABLE oc_series ALTER COLUMN modified_date SET NOT NULL;
  