Lookup values do not appear in merged rows
The key values may not match exactly between base and lookup CSV files.
Trim spaces and standardize casing in both key columns before merging.
Use this tool
Prepare the input and run the tool
Paste the base CSV, lookup CSV, and shared key column. Result: Copy or download the merged CSV.
Ready.
Merged CSV appears here.
Data handling: Files and pasted data are processed in this browser session.
Readiness details
What to check before using the result
Sample input
Base CSV plus lookup CSV with a shared SKU, ID, email, or order column.
Output preview
Combined CSV with lookup fields appended to matching base rows and conflicts made visible.
Expected checks
- Matched rows
- Unmatched keys
- Duplicate key values
- Column name conflicts
Artifacts you can produce
- Merged CSV output
Limits to review
- The tool cannot infer the correct match when key values are duplicated or inconsistent.
Practical notes
- Keep one untouched copy of each source CSV.
- Check unmatched rows before using the merged output downstream.
Tool guide
How to use CSV Merge by Key
Use this when one CSV has the main rows and another CSV has fields to add. The base CSV keeps its row order.
What this tool does
Join two CSV tables by a shared key and download the merged rows.
- Input
- Paste the base CSV, lookup CSV, and shared key column
- Output
- Copy or download the merged CSV
Tool advantages
- Runs in this page; the file or pasted data is not sent to a new app.
- Keeps the preview, report, and download in the same screen.
- Leaves you with an output you can copy, download, or check before using.
Step-by-step usage guide
- 1Paste the base and lookup CSVs.
- 2Enter the shared key column.
- 3Download the merged CSV.
Common errors and fixes
Duplicate lookup keys create ambiguous results
One base row cannot safely merge against multiple lookup rows with the same key.
Deduplicate the lookup CSV or choose a more specific key before downloading the merged output.
New columns overwrite existing names
The base CSV and lookup CSV may share column names other than the key.
Rename lookup columns before merging when you need to keep both versions.
When to use CSV Merge by Key
- You are checking files before an upload, import, share, or delivery.
- You want to confirm the result before sending it to another system.
- You need a copied result, downloaded file, or report that can be reviewed outside the page.
FAQ
Which table keeps the row order?
The base CSV keeps its row order. Matching lookup fields are added to each base row.
What happens to duplicate column names?
Lookup columns that conflict with base columns are prefixed with lookup_.