If a single data set was split into two files, both files typically:
Have the same columns/structure
Contain different rows (e.g., File 1 has rows 1–10,000; File 2 has rows 10,001–20,000)
The correct way to restore the original data set is to stack the rows from one file underneath the rows from the other. This operation is called:
Appending (or “union” in SQL terms):
You keep the same schema (same columns)
You increase the number of rows
Other options:
Merging usually joins based on a key column (like customer_id) to bring in additional columns.
Blending often refers to combining data from different sources on related keys, especially in BI tools.
Aggregating reduces detail (e.g., summing or grouping), which is the opposite of what we want here.
Since we simply want to rebuild the full data set from two vertical slices, the correct technique is Append (B).
CompTIA Data+ Reference (concept alignment):
CompTIA Data+ Official Exam Objectives – Domain on Data Mining / Data Preparation (combining datasets through appending vs merging).
CompTIA Data+ Official Study Guide – discussion of data append/union vs merge/join when preparing data.
