Merge CSV files with different column orders and remove duplicate IDs

The first file puts Order in column A. The second puts Amount there. Pasting one below the other would put prices in the order-number column.

Here is a small, repeatable example using three synthetic CSV files. It was checked in SheetSum’s public English tool on September 12, 2026. These are test records, not customer orders.

The three source files

Download a.csv · Download b.csv · Download c.csv

a.csv

b.csv — the same fields, in a different order

c.csv — a Note column instead of Amount

Match the columns before removing duplicates

Open Merge CSV and Excel files and choose all three files. Leave First row holds column names and Add source columns selected. Choose Union — keep every column, blanks where missing.

At this point, the result contains six rows. Amount appears in two source files and Note in one. A missing value stays blank; the tool does not invent it.

Enable Remove duplicate rows, then select Order as the comparison column. For this example, each order ID should appear once.

Do not skip that last selection. With source columns included, otherwise-identical records from different files have different source filenames. Comparing every column would not treat them as the same row.

Check the four remaining rows

The public tool displayed 3 tables → 4 rows × 6 columns · 2 duplicate rows removed. The sixth column is the source worksheet name; it is blank for these CSV inputs.

Notice what happened to order 00124: the earlier row from a.csv was kept. The note from c.csv was not added to it. Removing duplicates is not the same as combining the contents of duplicate records. If those rows represent separate order lines or meaningful updates, do not deduplicate on order ID alone.

Click Download Excel (.xlsx). In this test, reopening the downloaded file confirmed all four rows, the leading zeros in 00123, and the names José and 민수. Download the checked result.

Open full-size result screenshot

What this example does not demonstrate

The output is a table of text values. This test does not establish preservation of workbook formatting, formulas, charts, or date-display formats. It used CSV inputs; the XLSX download was checked separately. Different header names such as Order and Order number are not automatically understood to mean the same field.

The page was also inspected at a 390-pixel viewport without page-level horizontal overflow. That is a narrow desktop-browser check, not an iPhone or Android device test.

Disclosure: SheetSum and this guide have the same operator. Prepared with AI assistance and checked against recorded input files, the public tool, and the downloaded output. No search-traffic or productivity improvement was measured.

Merge CSV and Excel files