Power Query: Append vs. Merge Query
Hardik Srivastav
Two different shapes of "combine"
Append and Merge both combine two Power Query queries into one, and that's about where the similarity ends. Reaching for the wrong one doesn't usually throw an error — it just quietly produces the wrong table, which is worse.
Append: stacking rows
Append is a vertical combination. It takes two (or more) queries that share the same shape — the same columns, or close enough — and stacks their rows on top of each other into one longer table. Think of combining "Sales 2025" and "Sales 2026" into a single "Sales" table: same columns, more rows.
Columns that exist in one query but not the other come through as nulls for the rows from the query that didn't have them, rather than an error, which is a common source of "why is this column empty for half my rows" — Power Query matches columns by name, not by position, so a typo or renamed column in one of the source queries silently creates a duplicate column full of nulls instead of aligning with the existing one.
Merge: joining columns
Merge is a horizontal combination — a join, in database terms. It takes two queries and matches rows between them based on one or more key columns, then pulls additional columns from the second query onto the first. Think of adding a "Customer Segment" column from a Customers table onto a Sales table by matching on Customer ID.
Merge asks you to pick a join kind — Left Outer, Inner, Full Outer, and so on — which determines what happens to rows that don't find a match on the other side. The default, Left Outer, keeps every row from the first query and brings in matches from the second where they exist, leaving null where they don't. Picking Inner when you actually needed Left Outer is the other classic mistake here: rows silently disappear because they didn't have a match, and the row count just looks a little low rather than throwing anything that flags the problem.
The tell for which one you need
If the two queries describe the same kind of thing and you want more rows of it, that's Append. If one query describes something and the other adds more detail about that same thing via a shared key, that's Merge. Sales-2025 plus Sales-2026 is Append. Sales plus Customer-detail-by-ID is Merge.