sql语法，

SELECT grade, COUNT(grade)
FROM your_table_name
GROUP BY grade;

class QueryResult{
    String grade;
    @Embedded
    int total_count;

}

@Query("SELECT grade, COUNT(grade) as total_count FROM Students GROUP BY grade")
List<QueryResult> queryGroupedGrade();

给出另一个解决方案。如果您使用的是kotlin，那么您可以使用 groupBy 功能。https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/group-by.html
演示代码：
从sqlite获取数据

@Query("SELECT * FROM Students")
abstract fun queryGrade(): List<QueryResult>

提取数据并按等级分组

fun fetchGrade() {
    return dao.queryGrade().run{
        this.groupBy {it.grade}
    }
}

我认为这对其他开发人员很有用，所以我将我的最终解决方案发布到@simon5678上，这是我在评论中提到的上述答案的组合

@Query("SELECT grade, COUNT(grade) as total_count FROM Students GROUP BY grade")
fun queryGroupedGrade(): List<QueryResult>

data class QueryResult(

    var grade: String = "",

    @ColumnInfo(name = "total_count")
    var total_count: Int = 0
)