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From "Daniel Barclay (Drill) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-2431) Document behavior of floating point types
Date Fri, 13 Mar 2015 16:33:39 GMT

    [ https://issues.apache.org/jira/browse/DRILL-2431?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14360590#comment-14360590
] 

Daniel Barclay (Drill) commented on DRILL-2431:
-----------------------------------------------

> Values of float and double that ...fall short of the specified range cause an error.


Do you mean
1) less than the lowest value in the range (more negative), or
2) closer to zero (the absolute magnitude is less than the non-zero value of float or double
that is closest to zero)?

Since it's an error, than presumably it's case number 1 (underflow usually isn't an error,
but I don't know for Drill), but the wording seems ambiguous.

> Document behavior of floating point types
> -----------------------------------------
>
>                 Key: DRILL-2431
>                 URL: https://issues.apache.org/jira/browse/DRILL-2431
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Documentation
>    Affects Versions: 0.8.0
>            Reporter: Victoria Markman
>            Assignee: Kristine Hahn
>
>    Joining on columns of float and double data type produces confusing result. Drill
returns the same result as postgres. Part of me feels that we should not follow postgres blindly
in this case, removing implicit cast between float and double would be better choice.
>    At a minimum we should have a section in our documentation that discusses floating
point types and this is a good example on how things can go wrong if user does not understand
the behavior.
> Example of such a discussion in Postgres docs: http://www.postgresql.org/docs/9.1/static/datatype-numeric.html
> t1.csv
> {code}
> 997322.0399,997322.0399
> 982209.1438,982209.1438
> 997322,997322
> 982209,982209
> 963548,963548
> 959310,959310
> {code}
> t2.csv
> {code}
> 997322.0399,997322.0399
> 982209.1438,982209.1438
> 997322,997322
> 982209,982209
> 963548,963548
> 959310,959310
> {code}
> {code}
> create table t1(c_float, c_double) as
> select
>         case when columns[0] = '' then cast(null as float) else cast(columns[0] as float)
end,
>         case when columns[1] = '' then cast(null as double) else cast(columns[1] as double)
end
> from `t1.csv`;
> create table t2(c_float, c_double) as
> select
>         case when columns[0] = '' then cast(null as float) else cast(columns[0] as float)
end,
>         case when columns[1] = '' then cast(null as double) else cast(columns[1] as double)
end
> from `t2.csv`;
> 0: jdbc:drill:schema=dfs> select * from t1;
> +------------+------------+
> |  c_float   |  c_double  |
> +------------+------------+
> | 997322.06  | 997322.0399 |
> | 982209.1   | 982209.1438 |
> | 997322.0   | 997322.0   |
> | 982209.0   | 982209.0   |
> | 963548.0   | 963548.0   |
> | 959310.0   | 959310.0   |
> +------------+------------+
> 6 rows selected (0.05 seconds)
> 0: jdbc:drill:schema=dfs> select * from t2;
> +------------+------------+
> |  c_float   |  c_double  |
> +------------+------------+
> | 997322.06  | 997322.0399 |
> | 982209.1   | 982209.1438 |
> | 997322.0   | 997322.0   |
> | 982209.0   | 982209.0   |
> | 963548.0   | 963548.0   |
> | 959310.0   | 959310.0   |
> +------------+------------+
> 6 rows selected (0.044 seconds)
> {code}
> Implicit cast: looks incorrect, but in fact we can't expect this to work.
> {code}
> 0: jdbc:drill:schema=dfs> select * from t1, t2 where t1.c_float = t2.c_double;
> +------------+------------+------------+------------+
> |  c_float   |  c_double  |  c_float0  | c_double0  |
> +------------+------------+------------+------------+
> | 959310.0   | 959310.0   | 959310.0   | 959310.0   |
> | 963548.0   | 963548.0   | 963548.0   | 963548.0   |
> | 982209.0   | 982209.0   | 982209.0   | 982209.0   |
> | 997322.0   | 997322.0   | 997322.0   | 997322.0   |
> +------------+------------+------------+------------+
> 4 rows selected (0.127 seconds)
> {code}
> Explicit cast: same
> {code}
> 0: jdbc:drill:schema=dfs> select * from t1, t2 where cast(t1.c_float as double) =
t2.c_double;
> +------------+------------+------------+------------+
> |  c_float   |  c_double  |  c_float0  | c_double0  |
> +------------+------------+------------+------------+
> | 959310.0   | 959310.0   | 959310.0   | 959310.0   |
> | 963548.0   | 963548.0   | 963548.0   | 963548.0   |
> | 982209.0   | 982209.0   | 982209.0   | 982209.0   |
> | 997322.0   | 997322.0   | 997322.0   | 997322.0   |
> +------------+------------+------------+------------+
> 4 rows selected (0.136 seconds)
> {code}



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