如何解决将sql查询转换为等效的spark查询
我在Java8上使用spark-sql-2.4.1v
。
我有如下的场景/摘要
Dataset<Row> df =//loaded data from a csv file
// this has columns like "code1","code2","code3","code4","code5","code6",and "class"
df.createOrReplaceTempView("temp_tab");
List<String> codesList = Arrays.asList("code1","code5"); // codes of interest to be calculated.
codesList.stream().forEach( code -> {
String query = "select "
+ " avg(" + code + ") as mean,"
+ "percentile(" + code +",0.25) as p25"
+ "from " + temp_tab
+ " group by class";
Dataset<Row> resultDs = sparkSession.sql(query);
});
如何使用functions.expr()和functions.agg()编写代码?
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