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https://issues.apache.org/jira/browse/IMPALA-7087?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16705568#comment-16705568
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Sahil Takiar commented on IMPALA-7087:
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The SQL Standard does allow assigning values to a lower scale, in which case
the least significant digits should be either truncated or rounded (the
decision is implementation dependent). MySQL, Postgres, and Hive round rather
than truncate (so 1.19 is rounded to 1.2).
Given that Hive, MySQL, and Postgres follow this behavior, and its defined in
the SQL Standard, I think its worth implementing. If there are no objections, I
will try to tackle it in this JIRA.
> Impala is unable to read Parquet decimal columns with lower precision/scale
> than table metadata
> -----------------------------------------------------------------------------------------------
>
> Key: IMPALA-7087
> URL: https://issues.apache.org/jira/browse/IMPALA-7087
> Project: IMPALA
> Issue Type: Sub-task
> Components: Backend
> Reporter: Tim Armstrong
> Assignee: Sahil Takiar
> Priority: Major
> Labels: decimal, parquet
>
> This is similar to IMPALA-2515, except relates to a different precision/scale
> in the file metadata rather than just a mismatch in the bytes used to store
> the data. In a lot of cases we should be able to convert the decimal type on
> the fly to the higher-precision type.
> {noformat}
> ERROR: File '/hdfs/path/000000_0_x_2' column 'alterd_decimal' has an invalid
> type length. Expecting: 11 len in file: 8
> {noformat}
> It would be convenient to allow reading parquet files where the
> precision/scale in the file can be converted to the precision/scale in the
> table metadata without loss of precision.
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