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Databricks Certified Data Engineer Associate · Databricks
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- Correct answer : A — Spark raises an `AnalysisException` because `union` requires both DataFrames to have the same number of columns A . `union` requires both DataFrames to have the same number of columns with compatible types by position, so a 6-column DataFrame combined with a 5-column DataFrame raises an analysis error before any rows are combined. B . `union` does not perform schema reconciliation or fill in missing columns with null; a column count mismatch causes an error rather than an automatic null-filled merge. C . `union` does not silently drop columns to make schemas match; it strictly requires the same column count up front and fails when that is not the case. D . The operation does not complete successfully with a mismatched column count, so there is no resulting DataFrame with a column silently removed from its schema.