A Column is having many repeated values which type of index you should create on this column, if you have to?

A Column is having many repeated values which type of index you should create on this column, if you have  to?
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For example, assume there is a motor vehicle database with numerous low-cardinality columns such as car_color,  car_make, car_model, and car_year. Each column contains less than 100 distinct values by themselves, and a b tree index would be fairly useless in a database of 20 million vehicles.
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