```ruby
require_relative '../query_modifier'

module ConceptQL
  module QueryModifiers
    module Gdm
      class ProviderQueryModifier < QueryModifier
        def self.provided_columns
          [:provider_id, :specialty_concept_id]
        end

        def self.has_required_columns?(cols)
          needed = [:practitioner_id, :context_id].sort
          found = needed & cols
          !found.empty?
        end

        def modified_query
          if dm.table_cols(source_table).include?(:context_id)
            query.from_self(alias: :c)
              .join(Sequel[:contexts_practitioners].as(:cp), context_id: :context_id)
              .select_all(:c)
              .select_append(Sequel[:cp][:practitioner_id].as(:provider_id))
              .select_append(Sequel[:cp][:specialty_type_concept_id].as(:specialty_concept_id))
          else
            query
              .select_all
              .select_append(Sequel[:practitioner_id].as(:provider_id))
              .select_append(Sequel[nil].as(:specialty_concept_id))
          end.from_self
        end

      end
    end
  end
end

```

Fix issue with Union and CTEs
user
```ruby
require_relative '../query_modifier'

module ConceptQL
  module QueryModifiers
    module Gdm
      class ProviderQueryModifier < QueryModifier
        def self.provided_columns
          [:provider_id, :specialty_concept_id]
        end

        def self.has_required_columns?(cols)
          needed = [:practitioner_id, :context_id].sort
          found = needed & cols
          !found.empty?
        end

        def modified_query
          if dm.table_cols(source_table).include?(:context_id)
            query.from_self(alias: :c)
              .join(Sequel[:contexts_practitioners].as(:cp), context_id: :context_id)
              .select_all(:c)
              .select_append(Sequel[:cp][:practitioner_id].as(:provider_id))
              .select_append(Sequel[:cp][:specialty_type_concept_id].as(:specialty_concept_id))
          else
            query
              .select_all
              .select_append(Sequel[:practitioner_id].as(:provider_id))
              .select_append(Sequel.cast(nil, :Bigint).as(:specialty_concept_id))
          end.from_self
        end

      end
    end
  end
end

```
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