Transforming panel data

A panel’s Transform is optional DuckDB SQL that runs in the browser (DuckDB-WASM) on the rows your query returns, before the chart renders them. Use it when the chart needs columns that don’t exist on the raw table as-is — most commonly, an encoded telemetry column that needs decoding and flattening.

A transform reshapes rows already returned by your query. It does not change what the query selects from the database — for that, edit the Build or QueryScript YAML tab.

When you need a transform

Situation	Example
A column holds an encoded array/object (bytea or base64 JSON)	`cell_voltages` as a base64-encoded JSON array
A single row holds an array you want as multiple chart points	96 cell voltages → 96 bar-chart bars
You want to scale, rename, or compute a derived value	`soc_1 * 100 AS soc_pct`
You want only the latest record, regardless of the dashboard’s time filter	Gauge/stat panels showing “current state”

If your query already returns plain numeric/timestamp columns in the shape the chart needs, skip the transform entirely.

Write and run a transform

Open the panel editor → Transform tab.
Write DuckDB SQL. Your query’s result rows are available as the table raw.
Click Run transform to execute it and preview the output.

The FROM raw reference and the note above the editor spell this out directly: raw is your query’s result rows, and whatever columns your final SELECT produces are what the chart’s field mappings see next.

Structured columns (decoding encoded telemetry)

If a column holds base64 or \x-hex encoded JSON (a common shape for bytea telemetry columns), mark it under Structured columns so it’s decoded to a real array/object before your transform SQL runs. Columns typed bytea are usually auto-detected and pre-selected.

Without this step, your transform SQL would be working against a raw encoded string instead of a queryable array — unnest() and struct/array indexing wouldn’t have anything to operate on.

Templates

The Templates dropdown inserts a starting point for three common shapes:

Template	Use for
Passthrough	No reshaping — just confirms the `raw → transform → chart` wiring
Unnest array column	Turn one array column into N rows (bar/line charts over an array, e.g. per-cell voltages)
Waveform overlay (12×50 struct)	Unroll a nested `[segment][sample]` matrix (e.g. multi-signal waveform captures) into `sample_idx`-indexed rows for an XY line chart

Pick one, then adjust column names to match your table.

The “latest record” pattern

Most transforms should start by pinning to the most recent row, so the panel shows current state regardless of what column names or time semantics the raw table uses:

WITH latest AS (
  SELECT * FROM raw ORDER BY event_ts DESC LIMIT 1
)
SELECT ...
FROM latest

The transform preview in the editor already fetches the latest available rows independent of the dashboard’s time filter — so Run transform works even on a dashboard set to a narrow “Live” window with no recent data. The saved panel, once on a dashboard, still queries within whatever time filter is active — see Troubleshooting: panel shows “No data”.

Example: unnest an array into bar-chart rows

Given a cell_voltages column holding a flat array of 96 floats, turn the latest row into 96 chartable rows:

WITH latest AS (
  SELECT * FROM raw ORDER BY event_ts DESC LIMIT 1
)
SELECT u.idx AS cell_idx, u.v AS cell_voltage
FROM latest, unnest(cell_voltages) WITH ORDINALITY AS u(v, idx)
ORDER BY u.idx

Run the transform and check Input columns / Output columns to confirm the shape:

cell_idx and cell_voltage are now available to map onto a chart — see Linking transforms to panels.

Scaling or renaming a column

A transform is also the place to do simple arithmetic or aliasing — no separate “computed column” feature needed:

WITH latest AS (
  SELECT * FROM raw ORDER BY event_ts DESC LIMIT 1
)
SELECT soc_1 * 100 AS soc_1_pct
FROM latest

Re-run the transform after any SQL edit — the Output columns list and the chart’s column pickers only reflect the last successful run.

Next step

Linking transforms to panels

Map cell_idx / cell_voltage (or any transform output) onto a bar chart, line chart, or gauge.

Getting started

Dataspaces

Console

Dashboards

Transforming panel data

When you need a transform

Write and run a transform

Structured columns (decoding encoded telemetry)

Templates

The “latest record” pattern

Example: unnest an array into bar-chart rows

Scaling or renaming a column

Next step

Linking transforms to panels

​When you need a transform

​Write and run a transform

​Structured columns (decoding encoded telemetry)

​Templates

​The “latest record” pattern

​Example: unnest an array into bar-chart rows

​Scaling or renaming a column

​Next step

Linking transforms to panels

When you need a transform

Write and run a transform

Structured columns (decoding encoded telemetry)

Templates

The “latest record” pattern

Example: unnest an array into bar-chart rows

Scaling or renaming a column

Next step