dsl case when

DSL中的case和when是用于在Spark SQL中进行条件判断和值映射的。在DSL中，case语句用于根据条件对某个列进行值映射。when语句用于指定条件和相应的值映射。下面是一个示例：

val result = spark.sql("""
    SELECT id, avg_score,
        CASE
            WHEN avg_score >= 90 THEN '优秀'
            WHEN avg_score >= 80 THEN '良好'
            WHEN avg_score >= 70 THEN '中等'
            ELSE '不及格'
        END AS 等级
    FROM table_name
""")

上述代码中，当avg_score大于等于90时，等级被映射为'优秀'；当avg_score大于等于80时，等级被映射为'良好'；当avg_score大于等于70时，等级被映射为'中等'；否则，等级被映射为'不及格'。这样，在查询结果中就会添加一列等级来表示每个id对应的平均分的等级。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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