The available listing describes “Combined Reaction Volume” as a SQL interview tutorial associated with Meta, but it does not reveal the actual prompt or schema. That means no exact answer can be verified—and the title alone is not enough to reconstruct one. Here’s how to reason about the problem without mistaking an illustrative query for Meta’s answer.
What is known about this SQL question?
A DEV Community database-topic listing includes a tutorial titled “Meta’s ‘Combined Reaction Volume’ SQL Question, Explained Simply,” credited to Rahman and tagged as SQL, interview, and tutorial content. The listing frames it as a Meta interview question; it is not evidence that Meta published, uses, or endorses the question.
The listing does not provide the interview prompt, tables, columns, requested output, or the meaning of “combined reaction volume.” Without those details, a definitive query would be guesswork.
Why the title is not enough to write the query
“Combined” could describe combining reaction categories, data from multiple sources, or something else specified in the missing prompt. The word “volume” does not establish whether the requested measure is a count, a sum of stored values, or another metric. Nor does the title say whether results should be grouped by user, post, date, or another dimension.
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A correct query depends on the prompt’s output grain—the unit represented by each result row—and on how reactions are stored. For example, category counts in separate columns require a different aggregation from one row per reaction. Combining records from multiple tables also requires knowing their join keys and whether a join might duplicate records.
How to solve it once you have the prompt
- Identify the requested result. Note exactly what one output row represents, which measure is requested, and any filters or date boundaries.
- Inspect the schema. Determine the relevant tables, columns, data types, and relationships. Establish whether reaction categories are columns, individual rows, or split across sources.
- Define “combined” from the prompt. Decide which categories or sources belong in the metric; do not infer them from the title.
- Choose the aggregation. Use the appropriate aggregate and group by the dimensions required for the output. Check how nulls and duplicate records should be treated.
- Validate the result. Test a small example by hand and confirm that joins have not multiplied rows and that the grouping matches the requested output grain.
Illustrative example—not the Meta prompt
Suppose a hypothetical table named post_reactions contains one row per reaction, with columns post_id and reaction_type. If a hypothetical task asks for a count of all reaction rows per post, the query could be:
SELECT post_id, COUNT(*) AS reaction_volume
FROM post_reactions
GROUP BY post_id;This example assumes each row is one reaction and that every reaction type should be counted. It does not establish that the original question uses this table design, asks for a count, or groups by post. If reaction totals are stored in separate category columns, or if the task combines multiple sources, the query would need to reflect that schema and the prompt’s definition instead.
Quick Recap
What to check before accepting an answer
- Does the query return the requested unit of output, such as one row per post or per user?
- Does its aggregation match how reaction data is represented?
- Are all included categories, sources, and filters specified by the prompt?
- Could a join duplicate reaction records?
- Does the query handle missing values in the way the task requires?
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