# Overwrite a column with a formula

Shape / columns

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

Replace the values of an existing column with the result of an expression or another column's values, adding no column.

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

## Status

Runs as a SQL step.

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

## The DuckDB step

replace a column in place with a formula

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 * REPLACE (round(amount * 1.2, 2) AS amount) FROM orders;
SELECT order_id, amount FROM result;
SELECT CASE WHEN ((SELECT list(column_name) FROM (DESCRIBE result)) = (SELECT list(column_name) FROM (DESCRIBE orders)) AND (SELECT amount FROM result WHERE order_id = 1) = 144 AND (SELECT sum(amount) FROM result) = 2280.89 AND (SELECT count(amount) FROM result) = 9) THEN 'as expected' ELSE error('amount was not replaced in place by amount times 1.2 with no column added') 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).

- EasyMorph: [`Modify column(s)`](https://help.easymorph.com/doku.php?id=transformations:replacecolumns) (read 2026-09-27)
- Apache Hop: [`Set field Value to a field`](https://hop.apache.org/manual/latest/pipeline/transforms/setvaluefield.html) (read 2026-09-27)
- Apache Hop: [`Set field value to a constant`](https://hop.apache.org/manual/latest/pipeline/transforms/setvalueconstant.html) (read 2026-09-27)
- Apache NiFi: [`UpdateRecord`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.UpdateRecord/) (read 2026-09-27)
- OpenRefine: [`Transform…`](https://openrefine.org/docs/manual/cellediting#transform) (read 2026-09-27)
- Pentaho Data Integration: [`Set Field Value`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27)
- Pentaho Data Integration: [`Set Field Value to a Constant`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27)
- Polars: [`DataFrame.replace_column`](https://docs.pola.rs/api/python/stable/reference/dataframe/modify_select.html) (read 2026-09-27)
- Power Query M: [`Table.TransformColumns`](https://learn.microsoft.com/en-us/powerquery-m/table-functions#transformation) (read 2026-09-27)
- Trifacta: [`Edit with formula`](https://help.alteryx.com/aac/en/trifacta-classic/reference/transformation-reference.html) (read 2026-09-27)
- Trifacta: [`Set Transform`](https://help.alteryx.com/aac/en/trifacta-classic/wrangle-language/language-appendices/transforms.html) (read 2026-09-27)
- VisiData: [`setcell-expr`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/expr.py#L115) (read 2026-09-23)
- VisiData: [`setcol-expr`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/expr.py#L114) (read 2026-09-23)
- VisiData: [`setcol-iter`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/expr.py#L116) (read 2026-09-23)