# Fill down or up

Shape / rows

fill down or up across rows, and the inverse, blank down

Page: <https://meridian.online/operations/fill-down-or-up>

## Status

Runs as a SQL step.

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

## The DuckDB step

fill down the last known value

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, region,
       last_value(region IGNORE NULLS) OVER (ORDER BY order_id ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS region_filled
FROM orders;
SELECT * FROM result;
SELECT CASE WHEN ((SELECT count(*) FILTER (WHERE region_filled IS NULL) = 0 AND max(region_filled) FILTER (WHERE order_id = 9) = 'west' FROM result)) THEN 'as expected' ELSE error('order 9 was not filled from order 8') END AS verdict;
```

It needs nothing installed beyond DuckDB itself.

## Variants

- Blank out repeated values: Erase a cell when it repeats the value above, keeping only the first of each run.
- Fill blanks from the nearest value: Replace each null with the nearest non-null value above or below it, optionally within groups.

## What other tools call it

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

- DuckDB: [`fill`](https://duckdb.org/docs/current/sql/functions/window_functions) (read 2026-09-27)
- Duckle: [`Backward Fill`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25)
- Duckle: [`Forward Fill`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25)
- EasyMorph: [`Fill down`](https://help.easymorph.com/doku.php?id=transformations:fillgaps) (read 2026-09-27)
- Apache Hop: [`Repeat fields`](https://hop.apache.org/manual/latest/pipeline/transforms/repeatfields.html) (read 2026-09-27)
- OpenRefine: [`Blank down`](https://openrefine.org/docs/manual/cellediting#fill-down-and-blank-down) (read 2026-09-27)
- OpenRefine: [`Fill down`](https://openrefine.org/docs/manual/cellediting#fill-down-and-blank-down) (read 2026-09-27)
- Polars: [`Expr.backward_fill`](https://docs.pola.rs/api/python/stable/reference/expressions/modify_select.html) (read 2026-09-27)
- Polars: [`Expr.forward_fill`](https://docs.pola.rs/api/python/stable/reference/expressions/modify_select.html) (read 2026-09-27)
- Power Query M: [`Table.ClearDown`](https://learn.microsoft.com/en-us/powerquery-m/table-cleardown) (read 2026-09-27)
- Power Query M: [`Table.FillDown`](https://learn.microsoft.com/en-us/powerquery-m/table-functions#transformation) (read 2026-09-27)
- Power Query M: [`Table.FillUp`](https://learn.microsoft.com/en-us/powerquery-m/table-functions#transformation) (read 2026-09-27)
- RapidMiner Studio: [`Replace Missing Values (Series)`](https://docs.rapidminer.com/latest/studio/operators/modeling/time_series/transformation/replace_missing_values.html) (read 2026-09-27)
- Tableau Prep: [`Fill Down`](https://help.tableau.com/current/prep/en-us/prep_multirow_calculations.htm) (read 2026-09-27)
- Tableau Prep: [`LAST_VALUE`](https://help.tableau.com/current/prep/en-us/prep_function_reference.htm) (read 2026-09-27)
- Trifacta: [`FILL Function`](https://help.alteryx.com/aac/en/trifacta-classic/wrangle-language/window-functions.html) (read 2026-09-27)
- VisiData: [`setcol-fill`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/fill.py#L36) (read 2026-09-23)