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CSV Merge by Key

Join two CSV tables by a shared key and download the merged rows.

Maintained by TaskReadyTools· Testing and correction method

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.

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AssumptionsThe tool cannot infer the correct match when key values are duplicated or inconsistent.

Ready.

Merged CSV appears here.
Data handling: This page processes only pasted text and form inputs 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

What this tool does not do

  • 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.

References and workflow

Open related workflow

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

Step-by-step usage guide

  1. 1Paste the base and lookup CSVs.
  2. 2Enter the shared key column.
  3. 3Download the merged CSV.

Common errors and fixes

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.

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.

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_.