Key Takeaways
- The free joiner combines two CSV files on a shared key, like a VLOOKUP across whole files.
- It supports inner, left, right and full outer joins, so unmatched rows are kept or dropped by choice.
- Both files stay in your browser and are never uploaded.
- For joins across many files or fuzzy keys, Flookup Data Wrangler brings matching into Google Sheets.
Introduction
You have your orders in one file and the customer details in another.
To answer a simple question, you need the two side by side.
The free CSV joiner and VLOOKUP tool combines two files on a shared key and pulls the matching columns together. Open the CSV joiner.
What Joining Two Files Means
A join needs one thing: a key column that identifies a row in each file. An order ID, an email address or a product code works well. Once you have that, the tool matches rows on the key and combines the columns you choose.
- Key column: the value that identifies a row, chosen separately in each file.
- Output columns: which columns from each side end up in the result.
- Join type: whether unmatched rows survive, and from which file.
The Four Join Types
The join type decides what happens to rows whose key does not appear on the other side:
- Full outer join: keeps every row from both files, matched where possible and blank on the side with no match.
- Inner join: keeps only rows whose key appears in both files, the strictest and most common choice.
- Left join: keeps every row from the first file and fills the second file's columns where a match exists.
- Right join: the mirror image, keeping every row from the second file.
A Worked Example
File A holds orders:
| order_id | |
|---|---|
| 1001 | alice@example.com |
| 1002 | bob@example.com |
File B holds customer details keyed by email:
| city | plan | |
|---|---|---|
| alice@example.com | Nairobi | Pro |
| carol@example.com | Kampala | Team |
Joining on email, an inner join returns just the order that matched:
| order_id | city | plan | |
|---|---|---|---|
| 1001 | alice@example.com | Nairobi | Pro |
A left join returns both orders, leaving the city and plan blank for the second one. A full outer join also brings in the customer with no order. That difference is the whole point of choosing a join type.
Joining Compared with VLOOKUP
VLOOKUP does one job well: for each lookup value, it returns a column from a reference table. A join does the same work across two whole files at once, and it goes further.
- A join works on a saved file rather than a live range, so it fits a one-off reconciliation.
- A join can keep unmatched rows from either file, so you can see what did not line up.
- A join can bring in many columns from both files in a single pass.
When your source is a spreadsheet and the lookup changes often, a formula still makes sense. When you have two exports and need the answer now, a join is faster and leaves a reusable record.
Privacy First
Both files are parsed in a background worker in your browser.
Nothing is uploaded, stored or logged, so you can join customer, payroll and vendor exports without a second thought.
How to Use It
- Load file A and file B, confirming the header setting for each.
- Choose the key column in each file, such as an ID or email.
- Pick the join type and the columns you want in the result.
- Press Join, review the matched rows and download the output.
Common Pitfalls
- Keys that look identical but differ: trailing spaces or letter case make two keys unequal. Trim and standardise the key column before joining.
- Duplicate keys: if a key repeats in either file, each pairing is produced. Deduplicate first if you expected one row per key.
- Choosing the wrong key: a display name is a poor key because two people can share it. Prefer an ID or email.
- Expecting fuzzy matches: a join is exact. For near-duplicate keys, reach for the fuzzy matching tool first.
Beyond Two Files
The joiner combines two files on one exact key. When you need to reconcile many files, match on fuzzy keys or merge records that differ by a typo, the Flookup Data Wrangler add-on brings matching and merge workflows into Google Sheets. See the data cleaning tools for details.
Joining Two Files Should Not Need a Formula Column
A join is one of the most common data tasks there is and it should take seconds, not a spreadsheet full of VLOOKUPs that break when a column moves. The CSV joiner gives you inner, left, right and full outer joins between two files, with every unmatched row accounted for.
Both files stay on your device, so exports from your CRM, ERP or billing system can be combined without a second thought.
For recurring reconciliations or fuzzy keys, Flookup Data Wrangler brings the same matching engine into Google Sheets with workflow templates.