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Databricks Certified Associate Developer for Apache Spark · Databricks
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- approx_count_distinct uses HyperLogLog++ and is dramatically faster than exact countDistinct on billions of rows, with configurable error (default ~5%). Use the current snake_case F.approx_count_distinct — the old camelCase F.approxCountDistinct is only a deprecated (since Spark 2.1.0) alias for it. Option B counts rows, not distinct. Option C gives a global distinct count. Option D is anti-pattern.