# Copy a column

Shape / columns

A variant of [Add a calculated column](https://meridian.online/operations/add-a-calculated-column).

Add a copy of an existing column under a new name.

Page: <https://meridian.online/operations/add-a-calculated-column/copy-a-column>

## Status

Runs as a SQL step.

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

## The DuckDB step

add a copy of a column under a new name

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 *, amount AS amount_copy FROM orders;
SELECT order_id, amount, amount_copy FROM result;
SELECT CASE WHEN ((SELECT list(column_name) FROM (DESCRIBE result)) = (SELECT list(column_name) FROM (DESCRIBE orders)) || ['amount_copy'] AND (SELECT count(*) FILTER (WHERE amount_copy IS DISTINCT FROM amount) FROM result) = 0 AND (SELECT sum(amount_copy) FROM result) = 1900.74) THEN 'as expected' ELSE error('amount_copy was not a copy of amount beside the original columns') 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).

- Power Query M: [`Table.DuplicateColumn`](https://learn.microsoft.com/en-us/powerquery-m/table-functions#column-operations) (read 2026-09-27)
- RapidMiner Studio: [`Generate Copy`](https://docs.rapidminer.com/latest/studio/operators/blending/attributes/generation/generate_copy.html) (read 2026-09-27)
- Apache SeaTunnel: [`Copy`](https://seatunnel.apache.org/docs/2.3.13/transforms/copy) (read 2026-09-27)
- Tableau Prep: [`Duplicate Field`](https://help.tableau.com/current/prep/en-us/prep_clean.htm) (read 2026-09-27)
- VisiData: [`addcol-source`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/sheets.py#L1328) (read 2026-09-23)