Join two CSV tables by a key

How it works

Match exact parsed key strings using a map. A left join preserves unmatched left rows; an inner join keeps matches only. Repeated matching keys produce every matching pair.

Input definitions

Left CSV: Plain text; maximum 200,000 characters.
Right CSV: Plain text; maximum 200,000 characters.
Left key column: Enter the value in the labeled unit.
Right key column: Enter the value in the labeled unit.
Join type: Choose Left join / Inner join.

A worked example

Left CSV: id,name 1,Ada 2,Lin
Right CSV: id,city 1,London 3,Paris
Left key column: id
Right key column: id
Join type: Left join

2 joined rows

Assumptions & limits

Plain text on your device, with no remote fetch. CSV input is comma-separated with unique nonempty headers, at most 1,000 rows and 50 columns; downloads escape spreadsheet formula prefixes.

Sources & review

Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.

https://www.papaparse.com/docs ↗

Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.

Common questions

Why can joining two CSV tables create more rows than either input?

A key repeated on both sides creates multiple matching pairs. This tool preserves that behavior, labels columns with left/right prefixes and limits output to 10,000 rows.

How does Join two CSV tables by a key work?

Match exact parsed key strings using a map. A left join preserves unmatched left rows; an inner join keeps matches only. Repeated matching keys produce every matching pair.

What are the limits of Join two CSV tables by a key?

Plain text on your device, with no remote fetch. CSV input is comma-separated with unique nonempty headers, at most 1,000 rows and 50 columns; downloads escape spreadsheet formula prefixes.

How do I keep the full worksheet?

Run the tool and choose Download file. The on-page table is a preview and may show only the first 20 rows; the downloaded file contains the full result. CSV downloads escape spreadsheet formula prefixes. Inputs and files are processed on your device.