Join CSV Files with SQL

Join two or more CSV files with SQL JOIN: inner, left, right or full. Runs in your browser with DuckDB and nothing is uploaded.

Quick answer: Add files, write SQL, download the result.

How to use the Join CSV Files with SQL

Add files, write SQL, download the result.

SQL on Your Files lets you query CSV, Excel, JSON and Parquet files with real SQL, without installing a database or a tool like DBeaver. Add one or more files, each becomes a table, then write SELECT, JOIN, GROUP BY, window functions and more. It uses DuckDB, a fast analytics database that runs inside your browser, so your files stay on your device. The SQL engine itself (about 30 MB) is downloaded once from a CDN the first time you run a query.

Add one or more files
Write a SQL query using the table names
Run it and download the result

Tips

Add two files and use JOIN to combine them on a key.
Put column names that contain spaces in double quotes.
Use LIMIT while you test a query on a big file.
Queries only read your data. They never change your original files.
Very large files can run out of browser memory; filter or split them first.

Example

Input: orders.csv + customers.csv

Output: joined result

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Who uses Data Utility

Frequently asked questions · Data format benchmark

Frequently asked questions

How do I join two CSV files with SQL?

Add both files, then write SELECT with JOIN ... ON between the two table names. For a point-and-click join, use Data Transformation.

Which SQL does it use?

DuckDB SQL, which is close to PostgreSQL. Joins, aggregates, window functions, CTEs and date functions all work.

Does it work offline?

Not the first time, because the SQL engine is downloaded when you first run a query.

Can I run SQL on a CSV file without a database?

Yes. Add the file, write a query such as SELECT * FROM my_file WHERE amount > 100, and run it. It uses DuckDB in your browser, so there is nothing to install and the file is not uploaded.

SQL on Your Files: Query CSV, Excel and Parquet: Run SQL on CSV, Excel, JSON and Parquet files in your browser with DuckDB. SELECT, JOIN, GROUP BY and more. Nothing to install and your files are never uploaded.
Query a CSV File with SQL: Query a CSV file with SQL online. Filter, group, sort and join with DuckDB in your browser. No database, no install and no upload.
Run SQL on an Excel File: Run SQL queries on an Excel file without importing it into a database. Join sheets from different files and download the result.
Query Parquet Files Online: Open and query Parquet files with SQL in your browser. Preview, filter, aggregate and export to CSV without installing anything.
DuckDB in Your Browser: Use DuckDB in your browser with no setup. Drop in CSV, Excel, JSON or Parquet files and run analytical SQL on your own computer.