Some questions about Table API and FlinkSQL

[Anton Mushin]

Hello all,

I have some questions about work with FlinkSQL.



1)    I'm want calculate average for column values:



val env = ExecutionEnvironment.getExecutionEnvironment
val tEnv = TableEnvironment.getTableEnvironment(env, config)
val ds = env.fromElements(
      (1.0f, 1),
      (2.0f, 2)).toTable(tEnv)
    tEnv.registerTable("MyTable", ds)
    val sqlQuery="select avg(_1), avg(_2) from MyTable"
    tEnv.sql(sqlQuery).toDataSet[Row].collect().foreach(x=>print(s"$x "))



As result I'm getting: "1.5,1 ". But I expected: "1.5,1.5 "

Why is for columns like integer types avg function is return result as integer? 
Where is described this behavior?​​



2) I wanted calculate stddev_pop function like as sequences sql aggregate 
functions, how it is describe in calcite javadocs: 
https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/rules/AggregateReduceFunctionsRule.java#L64



val ds = env.fromElements(

      (1.0f, 1),

      (1.0f, 2)).toTable(tEnv)

    tEnv.registerTable("MyTable", ds)



val sqlQuery = "SELECT " +

      "SQRT((SUM(a*a) - SUM(a)*SUM(a)/COUNT(a))/COUNT(a)) "+

      "from (select _1 as a from MyTable)"

tEnv.sql(sqlQuery).toDataSet[Row].collect().foreach(print)

​

I got exception:



        org.apache.flink.runtime.client.JobExecutionException: Job execution 
failed.

.......

    Caused by: java.lang.Exception: The user defined 'open(Configuration)' 
method in class org.apache.flink.api.table.runtime.FlatMapRunner caused an 
exception: Table program cannot be compiled. This is a bug. Please file an 
issue.

         at 
org.apache.flink.runtime.operators.BatchTask.openUserCode(BatchTask.java:1337)

         at 
org.apache.flink.runtime.operators.chaining.ChainedFlatMapDriver.openTask(ChainedFlatMapDriver.java:47)

.....

    Caused by: org.codehaus.commons.compiler.CompileException: Line 59, Column 
57: No applicable constructor/method found for actual parameters "float, 
java.math.BigDecimal"; candidates are: "public static double 
org.apache.calcite.runtime.SqlFunctions.power(long, java.math.BigDecimal)", 
"public static double org.apache.calcite.runtime.SqlFunctions.power(long, 
long)", "public static double 
org.apache.calcite.runtime.SqlFunctions.power(double, double)"

         at 
org.codehaus.janino.UnitCompiler.compileError(UnitCompiler.java:10062)

         at 
org.codehaus.janino.UnitCompiler.findMostSpecificIInvocable(UnitCompiler.java:7476)



In this time if I am execute for int column ('_2') i getting result is equals 
'0.0'

What am I doing wrong?



Best regards,

Anton Mushin