CSV comparison by key helps answer a different question from line-by-line text comparison. A text comparison asks what changed at each location in the file. A keyed comparison asks what changed in the record identified by a particular value.
If yesterday's export is sorted by ID and today's is sorted by name, many lines can differ while the records themselves remain the same. A large difference report may then be showing movement rather than edits.
Choose the question before the comparison
For a sample inventory file, you might want to know whether product P-041 changed its description. Its position in the export is secondary. For a time-ordered event log, sequence can be essential. Sorting the log away would discard part of the information you want to compare.
Write the question explicitly. “Which products changed?” suggests record matching. “Did the event sequence change?” requires attention to order as well as values.
Text Compare is useful when the textual sequence is the object of the review. It is less useful as an explanation of record changes when a CSV export has merely been reordered.
The key must identify the record you mean
A name is often a weak key because it can repeat or change. A stable source-provided identifier may be more appropriate. Check uniqueness rather than assuming that a column called ID guarantees it.
If the key itself changes, a keyed comparison can interpret the result as an old record disappearing and a new one appearing. It may not know that a person renamed the identifier. Investigate that case separately instead of calling it a confirmed deletion and addition in the underlying system.
CSV Diff compares supported files by a key column. Read its duplicate-key behavior and other limits before choosing it for an important reconciliation.
The tool compares values in columns that appear in both tables. A newly added column therefore needs its own schema review. A clean value-difference result should not be described as proof that both files have identical structures.
Inspect the header sets first. Confirm that similarly named columns mean the same thing, and that a renamed column is not being treated as a missing one. Then review added, removed and changed records against the intended key.
For the inventory example, check product P-041 directly in both source files after reading the report. That spot check connects the reported change to the actual row. Keep the source exports available and document their dates or versions so the comparison can be repeated for the same inputs if somebody questions the result.