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From Anton Mushin <Anton_Mus...@epam.com>
Subject Some questions about Table API and FlinkSQL
Date Tue, 04 Oct 2016 16:04:20 GMT
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)"



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

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