[jira] [Commented] (DRILL-4618) random numbers generator function broken

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-4618?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15304412#comment-15304412 ] 

ASF GitHub Bot commented on DRILL-4618:
---------------------------------------

Github user StevenMPhillips commented on a diff in the pull request:

    https://github.com/apache/drill/pull/509#discussion_r64940411
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/expr/EvaluationVisitor.java ---
    @@ -811,7 +811,7 @@ public HoldingContainer visitFunctionCall(FunctionCall call, ClassGenerator<?> g
         @Override
         public HoldingContainer visitFunctionHolderExpression(FunctionHolderExpression holder, ClassGenerator<?> generator) throws RuntimeException {
           HoldingContainer hc = getPrevious(holder, generator.getMappingSet());
    -      if (hc == null) {
    +      if (hc == null || holder.isRandom()) {
    --- End diff --
    
    I think this change is not sufficient to cover all cases. If random() is just part of the expression, then this won't help. For example, the expression 2 * random().
    
    I think a better way to fix this would be to modify EqualityVisitor.visitFunctionHolderExpression() to return false if the function is random. That way any expression which contains a random function will never be considered equal to another expression.


> random numbers generator function broken
> ----------------------------------------
>
>                 Key: DRILL-4618
>                 URL: https://issues.apache.org/jira/browse/DRILL-4618
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Chunhui Shi
>            Assignee: Chunhui Shi
>
> File this JIRA based on the the bug description from Ted's email and discussion in dev mail list for record purpose:
> I am trying to generate some random numbers. I have a large base file (foo)
> this is what I get:
> 0: jdbc:drill:>  select floor(1000*random()) as x, floor(1000*random()) as
> y, floor(1000*rand()) as z from (select * from maprfs.tdunning.foo) a limit
> 20;
> +--------+--------+--------+
> |   x    |   y    |   z    |
> +--------+--------+--------+
> | 556.0  | 556.0  | 618.0  |
> | 564.0  | 564.0  | 618.0  |
> | 129.0  | 129.0  | 618.0  |
> | 48.0   | 48.0   | 618.0  |
> | 696.0  | 696.0  | 618.0  |
> | 642.0  | 642.0  | 618.0  |
> | 535.0  | 535.0  | 618.0  |
> | 440.0  | 440.0  | 618.0  |
> | 894.0  | 894.0  | 618.0  |
> | 24.0   | 24.0   | 618.0  |
> | 508.0  | 508.0  | 618.0  |
> | 28.0   | 28.0   | 618.0  |
> | 816.0  | 816.0  | 618.0  |
> | 717.0  | 717.0  | 618.0  |
> | 334.0  | 334.0  | 618.0  |
> | 978.0  | 978.0  | 618.0  |
> | 646.0  | 646.0  | 618.0  |
> | 787.0  | 787.0  | 618.0  |
> | 260.0  | 260.0  | 618.0  |
> | 711.0  | 711.0  | 618.0  |
> +--------+--------+--------+
> On this page, https://drill.apache.org/docs/math-and-trig/, the rand
> function is described and random() is not. But it appears that rand()
> delivers a constant instead (although a different constant each time the
> query is run) and it appears that random() delivers the same value when
> used multiple times in each returned value.
> This seems very, very wrong.
> The fault does not seem to be related to my querying a table:
> 0: jdbc:drill:> select rand(), random(), random() from (values (1),(2),(3))
> x;
> +---------------------+-----------------------+-----------------------+
> |       EXPR$0        |        EXPR$1         |        EXPR$2         |
> +---------------------+-----------------------+-----------------------+
> | 0.1347749257216052  | 0.36724556209765014   | 0.36724556209765014   |
> | 0.1347749257216052  | 0.006087161689924625  | 0.006087161689924625  |
> | 0.1347749257216052  | 0.09417099142512142   | 0.09417099142512142   |
> +---------------------+-----------------------+-----------------------+
> For reference, postgres doesn't have rand() and does the right thing with
> random().



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