scala - 在 spark-sql 中执行 SQL 语句

Question

我有一个格式如下的文本文件:

ID,Name,Rating
1,A,3
2,B,4
1,A,4

我想在 spark 中找到每个 ID 的平均评分。这是我到目前为止的代码，但它一直给我一个错误:

val Avg_data=spark.sql("select ID, AVG(Rating) from table")

ERROR: org.apache.sapk.sql.AnalysisException: grouping expressions sequence is empty, and 'table'.'ID' is not an aggregate function. Wrap '(avg(CAST(table.'Rating' AS BIGINT)) as 'avg(Rating)')' in windowing function(s).........

Answer 1

AVG() 是一个聚合函数，因此您也需要一个分组依据

val Avg_data=spark.sql("select ID, AVG(Rating) as average from table group by ID")

你应该有 Avg_data 作为

+---+-------+
|ID |average|
+---+-------+
|1  |3.5    |
|2  |4.0    |
+---+-------+