Combine Columns in Parquet Files Online
Combine multiple columns into one in Parquet files directly in your browser. Merge first name and last name, join address fields, or concatenate any columns with a custom separator — no upload required.
How to combine Columns in Parquet files
- Drop your file onto the upload area. The first two columns are ticked by default and the output name is set to both names joined by an underscore.
- Tick the columns to combine in the order you want them joined. Each ticked column shows its position (#1, #2, and so on), and the order follows your clicks, not the file's column order.
- Type the separator, such as a space, ", " or " - ", and set the output column name.
- Tick Remove source columns if you only want the combined column, then click Combine Columns.
- Check the preview and download the file in the same format.
Your file is processed locally in your browser and is never uploaded. The free limit is 50 MB per file; larger files work if your device has the memory for them.
Worked example
An international order export stores the delivery address across four columns. The courier's upload form wants one address line per parcel.
Input (Parquet)
Parquet file (binary, columnar) — shown as a table with its schema
| recipient | street | city | postcode | country |
|---|---|---|---|---|
| Priya Shah | 12 Cuba Street | Wellington | 6011 | New Zealand |
| Tom Walsh | 8 Quay Road | Cork | NULL | Ireland |
| Ines Duarte | Rua Augusta 40 | Lisboa | 1100-048 | Portugal |
Schema: recipient VARCHAR, street VARCHAR, city VARCHAR, postcode VARCHAR, country VARCHAR
Settings
- Columns, in click order: street, city, postcode, country
- Separator: ", "
- Output column name: full_address
- Remove source columns: ticked
Result
| recipient | full_address |
|---|---|
| Priya Shah | 12 Cuba Street, Wellington, 6011, New Zealand |
| Tom Walsh | 8 Quay Road, Cork, Ireland |
| Ines Duarte | Rua Augusta 40, Lisboa, 1100-048, Portugal |
Values are joined in the order the columns were ticked, with the separator between them. Tom's postcode is empty, and it is skipped along with its separator, so there is no ", ," gap. With the source columns removed, full_address takes the position of the last source column. Unticked columns such as recipient stay where they were.
Working with Parquet files
The combined column is always a string, whatever the source types. Joining an integer year and month gives text like "2026 4", not a date, and joining a DECIMAL(10,2) keeps both decimal places because the scale is part of the type. Timestamps join in the form 2026-04-11 08:15:32, and booleans join as true or false. A DOUBLE joins in its shortest form, so 2.50 is written as 2.5 inside the combined text.
Parquet keeps NULL separate from an empty string. A NULL source value is skipped with its separator, but an empty string is joined, which can leave a trailing separator such as "Cork, ". Removing source columns changes the schema of the output file, so leave them in place if the file feeds a table with a fixed layout and drop them later. The rest of the schema, including nested struct columns you did not tick, is written back unchanged.
Frequently Asked Questions
What type is the combined column in the Parquet output?
Always a string (VARCHAR). Cast it afterwards if you are building a key that should be numeric.
Why does my combined Parquet value end with a separator?
One of the source values is an empty string rather than NULL. Only NULLs are skipped. Use Find & Replace or Fill Empty Values to make the column consistent first.
What happens to empty (null) values when combining columns?
They are skipped, and so is the separator next to them. Combining "Cork", null and "Ireland" with ", " gives "Cork, Ireland". Empty strings are not null, so they are joined as-is.
Can I combine more than two columns, and control the order?
Yes. Tick as many columns as you need. They are joined in the order you tick them, shown as #1, #2 and so on next to each column name.
Can I leave the separator empty?
Yes. With an empty separator the values are joined directly, for example "AB" and "123" become "AB123".
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