# Spread nested fields into columns Shape / columns A variant of [Parse nested values](https://meridian.online/operations/parse-nested-values). Lift every field of a struct or object column into its own top-level column, one row still per row. Page: ## Status Runs as a SQL step. arcform carries it as a `sql:` step today. ## The DuckDB step spread the fields of a struct into top-level columns, one row per row It reads the `orders` table the proofs share. Create it first: ```sql CREATE TABLE orders AS SELECT * FROM (VALUES (1, 'Alice Ng', 'north', DATE '2026-01-03', 120.00, 'widget', 'a|b', '{"channel":"web","items":[1,2]}'), (2, 'alice ng', 'north', DATE '2026-01-05', 80.50, 'gadget', 'b', '{"channel":"shop","items":[3]}'), (3, 'Bob Okafor', 'south', DATE '2026-01-05', 300.00, 'widget', 'a|c', '{"channel":"web","items":[4,5,6]}'), (4, 'Carla Díaz', 'east', DATE '2026-01-09', NULL, 'gizmo', NULL, '{"channel":"web","items":[]}'), (5, 'Bob Okafor', 'south', DATE '2026-01-12', 45.25, 'gadget', 'c', '{"channel":"phone","items":[7]}'), (6, 'Dev Patel', 'west', DATE '2026-01-12', 510.00, 'widget', 'a', '{"channel":"web","items":[8,9]}'), (7, 'Carla Diaz', 'east', DATE '2026-01-20', 99.99, 'gizmo', 'b|c', '{"channel":"shop","items":[10]}'), (8, 'Dev Patel', 'west', DATE '2026-02-02', 510.00, 'widget', 'a', '{"channel":"web","items":[8,9]}'), (9, 'Eve Larsen', NULL, DATE '2026-02-03', 15.00, 'gadget', NULL, '{"channel":"web","items":[11]}'), (10, 'Alice Ng', 'north', DATE '2026-02-10', 220.00, 'gizmo', 'a|b|c', '{"channel":"phone","items":[12,13]}') ) t(order_id, customer, region, order_date, amount, product, tags, meta); ``` Then run the statement: ```sql CREATE TEMP TABLE raw AS SELECT order_id, meta FROM orders UNION ALL SELECT 11, NULL; CREATE TEMP TABLE result AS SELECT order_id, s.* FROM (SELECT order_id, from_json(meta, '{"channel":"VARCHAR","items":["INTEGER"]}') AS s FROM raw); SELECT * FROM result ORDER BY order_id; DESCRIBE result; SELECT CASE WHEN ((SELECT list(column_name) FROM (DESCRIBE result)) = ['order_id', 'channel', 'items'] AND (SELECT count(*) FROM result) = 11 AND (SELECT items FROM result WHERE order_id = 3) = [4, 5, 6] AND (SELECT count(*) FROM result WHERE order_id = 11 AND channel IS NULL AND items IS NULL) = 1) THEN 'as expected' ELSE error('the struct was not spread into a channel column and an items column with one row per row, or a missing struct lost its row') END AS verdict; ``` It needs nothing installed beyond DuckDB itself. ## What other tools call it Meridian's classification; an independent blind rating agreed on 95.7% of 324 rows (variant, version 3). - Alteryx Designer: [`XML Parse`](https://help.alteryx.com/current/en/designer/tools/parse/xml-parse-tool.html) (read 2026-09-27) - Apache DataFusion: [`unnest (struct)`](https://datafusion.apache.org/user-guide/sql/special_functions.html) (read 2026-09-27) - Duckle: [`Flatten`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25) - AWS Glue: [`Flatten`](https://docs.aws.amazon.com/glue/latest/dg/transforms-flatten.html) (read 2026-09-27) - AWS Glue: [`Simplify_ddb_json`](https://docs.aws.amazon.com/glue/latest/dg/aws-glue-api-crawler-pyspark-transforms-simplify-ddb-json.html) (read 2026-09-27) - AWS Glue: [`UnnestFrame`](https://docs.aws.amazon.com/glue/latest/dg/aws-glue-api-crawler-pyspark-transforms-UnnestFrame.html) (read 2026-09-27) - AWS Glue: [`unnest_ddb_json`](https://docs.aws.amazon.com/glue/latest/dg/aws-glue-api-crawler-pyspark-extensions-dynamic-frame.html) (read 2026-09-27) - KNIME Analytics Platform: [`JSON to Table`](https://api.hub.knime.com/nodes/*2xUDt4Z24aku4wiS?details=full) (read 2026-09-27) - Apache NiFi: [`FlattenJson`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.FlattenJson/) (read 2026-09-27) - Polars: [`DataFrame.unnest`](https://docs.pola.rs/api/python/stable/reference/dataframe/modify_select.html) (read 2026-09-27) - Power Query M: [`Table.ExpandRecordColumn`](https://learn.microsoft.com/en-us/powerquery-m/table-functions#transformation) (read 2026-09-27) - Talend: [`tExtractDynamicFields`](https://help.qlik.com/talend/en-US/components/8.0/processing/processing-component) (read 2026-09-27) - Trifacta: [`Unnest Transform`](https://help.alteryx.com/aac/en/trifacta-classic/wrangle-language/language-appendices/transforms.html) (read 2026-09-27) - Trifacta: [`Unnest elements`](https://help.alteryx.com/aac/en/trifacta-classic/reference/transformation-reference.html) (read 2026-09-27) - VisiData: [`contract-col`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L191) (read 2026-09-23) - VisiData: [`contract-col-depth`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L193) (read 2026-09-23) - VisiData: [`contract-cols`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L192) (read 2026-09-23) - VisiData: [`contract-cols-depth`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L194) (read 2026-09-23) - VisiData: [`expand-col`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L186) (read 2026-09-23) - VisiData: [`expand-col-depth`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L188) (read 2026-09-23) - VisiData: [`expand-cols`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L187) (read 2026-09-23) - VisiData: [`expand-cols-depth`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/expand_cols.py#L189) (read 2026-09-23)