# Combine columns into one

Shape / columns

concatenate several columns into one

Page: <https://meridian.online/operations/combine-columns-into-one>

## Status

Runs as a SQL step.

arcform carries it as a `sql:` step today.

## The DuckDB step

concatenate columns

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 result AS
SELECT order_id, concat_ws(' / ', region, product, order_id) AS label FROM orders;
SELECT * FROM result;
SELECT CASE WHEN ((SELECT max(label) FILTER (WHERE order_id = 1) = 'north / widget / 1' AND max(label) FILTER (WHERE order_id = 9) = 'gadget / 9' FROM result)) THEN 'as expected' ELSE error('the label did not join its parts and skip the missing region') END AS verdict;
```

It needs nothing installed beyond DuckDB itself.

## What other tools call it

Meridian's classification; an independent blind rating agreed on 86.2% of 312 rows (exact class, version 2).

- Duckle: [`Concat`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25)
- AWS Glue: [`Concatenate Columns`](https://docs.aws.amazon.com/glue/latest/dg/transforms-concatenate-columns.html) (read 2026-09-27)
- Apache Hop: [`Concat fields`](https://hop.apache.org/manual/latest/pipeline/transforms/concatfields.html) (read 2026-09-27)
- Ibis: [`StringConcat`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/strings.py) (read 2026-09-27)
- Ibis: [`StringJoin`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/strings.py) (read 2026-09-27)
- KNIME Analytics Platform: [`Column Combiner`](https://api.hub.knime.com/nodes/*_3lbfRYUi6sJ5AQm?details=full) (read 2026-09-27)
- OpenRefine: [`Join columns…`](https://openrefine.org/docs/manual/columnediting#join-columns) (read 2026-09-27)
- Pentaho Data Integration: [`Concat Fields`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27)
- Polars: [`concat_str`](https://docs.pola.rs/api/python/stable/reference/expressions/functions.html) (read 2026-09-27)
- Polars: [`format`](https://docs.pola.rs/api/python/stable/reference/expressions/functions.html) (read 2026-09-27)
- Power Query M: [`Combiner functions`](https://learn.microsoft.com/en-us/powerquery-m/combiner-functions) (read 2026-09-27)
- Power Query M: [`Table.CombineColumns`](https://learn.microsoft.com/en-us/powerquery-m/table-functions#transformation) (read 2026-09-27)
- RapidMiner Studio: [`Combine Documents`](https://docs.rapidminer.com/latest/studio/operators/extensions/Text%20Processing/transformation/combine_documents.html) (read 2026-09-27)
- RapidMiner Studio: [`Generate Concatenation`](https://docs.rapidminer.com/latest/studio/operators/blending/attributes/generation/generate_concatenation.html) (read 2026-09-27)
- Talend: [`tWriteDelimitedFields`](https://help.qlik.com/talend/en-US/components/8.0/processing/processing-component) (read 2026-09-27)
- Talend: [`tWritePositionalFields`](https://help.qlik.com/talend/en-US/components/8.0/processing/processing-component) (read 2026-09-27)
- Trifacta: [`Merge Transform`](https://help.alteryx.com/aac/en/trifacta-classic/wrangle-language/language-appendices/transforms.html) (read 2026-09-27)
- Trifacta: [`Merge columns`](https://help.alteryx.com/aac/en/trifacta-classic/reference/transformation-reference.html) (read 2026-09-27)
- VisiData: [`join-cols`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/metasheets.py#L115) (read 2026-09-23)