SPARKPOND / GUIDE
How to Merge CSV Files with Different Columns
Files can be merged when their headers are mapped to a common output schema rather than matched by position.
Problem symptoms
- Values shift into the wrong columns.
- One file adds optional fields.
Why it happens
- Column order changed.
- Teams renamed the same concept.
- Exports evolved over time.
Example before and after
Before
a.csv: id,name b.csv: name,id,city
After
id,name,city 1,Ada, 2,Linus,Helsinki
Procedure
- Inspect every header set.
- Choose strict match or schema union.
- Map renamed fields.
- Preview missing cells and file order, then export.
Common mistakes
- Appending by column position.
- Treating merge as a key-based join.
Other possible solutions
- Use Join CSV when rows must be matched rather than appended.
Important limitations
- Meaningfully different columns cannot be mapped automatically.