[1.1 基数（CARDINALITY)](1.1%E5%9F%BA%E6%95%B0%EF%BC%88CARDINALITY.md) [1.2 选择性（SELECTIVITY)](1.2%E9%80%89%E6%8B%A9%E6%80%A7%EF%BC%88SELECTIVITY.md)