# Pack columns into a nested value Shape / columns A variant of [Parse nested values](https://meridian.online/operations/parse-nested-values). Combine several columns of each row into one struct, list, JSON, XML or Avro column. Page: ## Status Runs as a SQL step. arcform carries it as a `sql:` step today, with the `avro` extension. ## The DuckDB step pack several columns of each row into one struct, list, JSON, XML and Avro column ```sql CREATE TEMP TABLE items AS SELECT * FROM (VALUES (1, 'Alice Ng', 120.00, 'north', 'widget'), (2, 'Tom & ', NULL, NULL, 'gizmo') ) t(id, customer, amount, region, product); -- each text is escaped (& first, then < and >) before it is put between tags; a missing value gives an empty tag CREATE MACRO esc(x) AS replace(replace(replace(x, '&', '&'), '<', '<'), '>', '>'); CREATE TEMP TABLE result AS SELECT id, {'customer': customer, 'amount': amount} AS as_struct, [region, product] AS as_list, to_json({'customer': customer, 'amount': amount}) AS as_json, '' || coalesce(esc(customer), '') || '' || coalesce(amount::VARCHAR, '') || '' AS as_xml FROM items; SELECT * FROM result ORDER BY id; DESCRIBE result; SELECT CASE WHEN ((SELECT list(column_name) FROM (DESCRIBE result)) = ['id', 'as_struct', 'as_list', 'as_json', 'as_xml'] AND (SELECT as_struct.customer || '/' || as_struct.amount FROM result WHERE id = 1) = 'Alice Ng/120.00' AND (SELECT as_list FROM result WHERE id = 2) = [NULL, 'gizmo'] AND (SELECT as_json::VARCHAR FROM result WHERE id = 2) = '{"customer":"Tom & ","amount":null}' AND (SELECT as_xml FROM result WHERE id = 2) = 'Tom & <Jerry>' AND (SELECT as_xml FROM result WHERE id = 1) = 'Alice Ng120.00') THEN 'as expected' ELSE error('customer and amount were not packed into one struct, one JSON and one escaped XML column, or region and product into one list') END AS verdict; -- Avro: the packed struct is written to an Avro file and read back as one column COPY (SELECT id, as_struct FROM result) TO '/packed.avro' (FORMAT avro); SELECT CASE WHEN ((SELECT count(*) FROM read_avro('/packed.avro') WHERE as_struct.customer = 'Tom & ' AND as_struct.amount IS NULL) = 1 AND (SELECT count(*) FROM read_avro('/packed.avro')) = 2) THEN 'as expected' ELSE error('the packed struct did not come back from the Avro file as one column') END AS verdict; ``` Replace `` with a directory of your own that you can write to before running the statement. The statement writes `packed.avro` itself, in ``. It needs the `avro` extension. ## What other tools call it Meridian's classification; an independent blind rating agreed on 95.7% of 324 rows (variant, version 3). - Alteryx Designer: [`JSON Build`](https://help.alteryx.com/current/en/designer/tools/laboratory/json-build-tool.html) (read 2026-09-27) - Apache DataFusion: [`Struct Functions`](https://datafusion.apache.org/user-guide/sql/scalar_functions.html) (read 2026-09-27) - Duckle: [`Merge Objects`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25) - EasyMorph: [`Construct JSON`](https://help.easymorph.com/doku.php?id=transformations:constructjson) (read 2026-09-27) - Apache Hop: [`Add XML`](https://hop.apache.org/manual/latest/pipeline/transforms/addxml.html) (read 2026-09-27) - Apache Hop: [`Avro encode`](https://hop.apache.org/manual/latest/pipeline/transforms/avro-encode.html) (read 2026-09-27) - Ibis: [`Array`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/arrays.py) (read 2026-09-27) - Ibis: [`StructColumn`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/structs.py) (read 2026-09-27) - KNIME Analytics Platform: [`Column to XML`](https://api.hub.knime.com/nodes/*VqkSwDBKksqolRKh?details=full) (read 2026-09-27) - KNIME Analytics Platform: [`Columns to Collection`](https://api.hub.knime.com/nodes/*eNgVOpmMFNJq3Jie?details=full) (read 2026-09-27) - KNIME Analytics Platform: [`Columns to JSON`](https://api.hub.knime.com/nodes/*S5sWr2sm-SjOA14S?details=full) (read 2026-09-27) - KNIME Analytics Platform: [`JSON Column Combiner`](https://api.hub.knime.com/nodes/*YWufNYG_cCOXV2VP?details=full) (read 2026-09-27) - KNIME Analytics Platform: [`Nominal Probability Distribution Creator`](https://api.hub.knime.com/nodes/*TD93rewy2eMlDiSJ?details=full) (read 2026-09-27) - KNIME Analytics Platform: [`XML Column Combiner`](https://api.hub.knime.com/nodes/*iY4Ln0a0nzW73ykY?details=full) (read 2026-09-27) - Apache NiFi: [`AttributesToCSV`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.AttributesToCSV/) (read 2026-09-27) - Apache NiFi: [`AttributesToJSON`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.AttributesToJSON/) (read 2026-09-27) - Pentaho Data Integration: [`Add XML`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27) - Polars: [`DataFrame.to_struct`](https://docs.pola.rs/api/python/stable/reference/dataframe/export.html) (read 2026-09-27) - Polars: [`concat_arr`](https://docs.pola.rs/api/python/stable/reference/expressions/functions.html) (read 2026-09-27) - Polars: [`concat_list`](https://docs.pola.rs/api/python/stable/reference/expressions/functions.html) (read 2026-09-27) - Polars: [`list`](https://docs.pola.rs/api/python/stable/reference/expressions/functions.html) (read 2026-09-27) - Polars: [`struct`](https://docs.pola.rs/api/python/stable/reference/expressions/functions.html) (read 2026-09-27) - Power Query M: [`Table.CombineColumnsToRecord`](https://learn.microsoft.com/en-us/powerquery-m/table-functions#transformation) (read 2026-09-27) - RapidMiner Studio: [`Data To JSON`](https://docs.rapidminer.com/latest/studio/operators/extensions/Text%20Processing/utility/data_to_json.html) (read 2026-09-27) - Talend: [`tWriteAvroFields`](https://help.qlik.com/talend/en-US/components/8.0/processing/processing-component) (read 2026-09-27) - Talend: [`tWriteDynamicFields`](https://help.qlik.com/talend/en-US/components/8.0/processing/processing-component) (read 2026-09-27) - Talend: [`tWriteJSONField`](https://help.qlik.com/talend/en-US/components/8.0/processing/processing-component) (read 2026-09-27) - Talend: [`tWriteXMLField`](https://help.qlik.com/talend/en-US/components/8.0/xml/xml-component) (read 2026-09-27) - Talend: [`tWriteXMLFields`](https://help.qlik.com/talend/en-US/components/8.0/processing/processing-component) (read 2026-09-27) - Trifacta: [`Nest Transform`](https://help.alteryx.com/aac/en/trifacta-classic/wrangle-language/language-appendices/transforms.html) (read 2026-09-27) - Trifacta: [`Nest columns`](https://help.alteryx.com/aac/en/trifacta-classic/reference/transformation-reference.html) (read 2026-09-27) - VisiData: [`contract-source-cols`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L196) (read 2026-09-23)