A silver table of customer contacts is usable as long as a customer can be reached by at least one channel. Rows where BOTH email and phone are NULL must be removed. Rows where only one of the two is NULL must be kept, with the NULL value preserved in place. ```python bronze = spark.read.table("catalog.crm.bronze_contacts") silver = <drop rule> ``` Which dropna call implements this rule?
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Correct answer: silver = bronze.dropna(how='all', subset=['email', 'phone'])
Reference: https://docs.databricks.com/aws/en/pyspark/reference/functions
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Official Answer (B): silver = bronze.dropna(how='all', subset=['email', 'phone'])
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