Practical task An SQL query on 80 million messages creates duplicates after JOIN. Which action is best to start first? - Check the cardinality of the JOIN, keys, and execution plan before optimization. - Create an index on one join field. - Export the result to CSV and remove duplicates in Python. - Always add DISTINCT to all columns. - Add DISTINCT after verifying the result on a sample. - Check the join keys and the uniqueness of both tables.