Assumptions
- Columns are matched by name. Two names for the same field stay separate columns, so align them in the source files first.
- Each worksheet becomes one table. In a merged range only the top-left cell carries the value.
- Duplicate comparison uses trimmed text and keeps the first row seen.
- Everything runs in memory, 25 MB per file. Nothing is stored or transmitted.
How it is calculated
- Files are read in your browser. CSV encoding is detected automatically; a workbook is split into one table per sheet.
- Column names from every table are collected and grouped, ignoring spacing and letter case.
- The chosen mode decides the final column list, and every row is rearranged into that order.
- With duplicate removal on, rows sharing the key columns collapse into one, and the result is written as CSV or as a text-typed .xlsx.
Examples
Common mistakes
- Align your headers first. "Order no" and "Order no" merge because only spacing differs, but "Order no" and "Order number" stay apart.
- Read the column check table before downloading. A column that appears in only one file usually means a typo in a header.
- Duplicate removal cannot be undone. Keep the source files and confirm the removed count looks right before saving.
FAQ
Do the files need the same column order?
No. Columns are matched by name, not by position. Leading and trailing spaces, repeated spaces and letter case are ignored, so "Email", "email" and " Email " are treated as one column. A column that appears in only some files is filled with blanks under the union setting.
Union, intersection or first table — which do I want?
Union keeps every column that appears anywhere, so nothing is lost; use it when the files are near-identical exports with a few extra fields. Intersection keeps only the columns every file has, which gives a clean rectangular table. First table uses the column layout of the first table and drops extra columns from the others, which is handy when one file is the canonical template. The tool lists which columns get left out.
How are duplicates decided?
By default a row is a duplicate only when every column matches. For files keyed on an order number or an email address, tick just that column instead. Values are compared after trimming surrounding spaces, and turning on case-insensitive matching also treats A@X.COM and a@x.com as the same. The first occurrence is the one kept.
What happens to a workbook with many sheets?
Each sheet is loaded as its own table and listed separately. A single file with twelve monthly sheets therefore merges into one flat table on its own. Turn on the source columns to keep a record of which file and sheet each row came from.
Will leading zeros survive?
In the Excel download, yes: every cell is written as text, so 00123 stays 00123. The CSV also writes the value as-is, but Excel converts it back to a number when you double-click a CSV, so choose the .xlsx download if the result is going straight into Excel.
Are my files uploaded?
No. Reading, merging and saving all happen in your browser. Neither the contents nor the file names leave your device.