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https://issues.apache.org/jira/browse/DRILL-8071?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17458822#comment-17458822
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PJ Fanning commented on DRILL-8071:
-----------------------------------
I scaled back the scope of this issue to just what was covered in the linked PR.
I removed this from the description:
The existing ExcelBatchReader uses the raw data values from the cells. This raw
data ignores formatting set on the cells. As an example, numbers and dates are
stored as doubles. With the POI DataFormatter, you can get the cell style
applied so that the data will appear as it does when you view the data in Excel
itself.
[https://poi.apache.org/apidocs/dev/org/apache/poi/ss/usermodel/DataFormatter.html#formatCellValue-org.apache.poi.ss.usermodel.Cell-]
A big number like 123456789.987654 could be stored as double that is more like
123456789.9876539999999 when represented in decimal format (because this might
be the closest match that double can represent). The cell format could say that
cell has 6 decimal places after the decimal point so the formatter would round
the number back to the value that it displayed in Excel as.
Even if you choose not to use the DataFormatter, you have unprotected calls to
`cell.getNumericCellValue()` and that could easily throw an exception (if the
data is not stored a number). Even `cell.getStringCellValue()` can throw an
exception - for similar reasons.
> format-excel data parsing should use POI code
> ---------------------------------------------
>
> Key: DRILL-8071
> URL: https://issues.apache.org/jira/browse/DRILL-8071
> Project: Apache Drill
> Issue Type: Improvement
> Components: Execution - Data Types
> Affects Versions: 1.19.0
> Reporter: PJ Fanning
> Priority: Major
>
> There is also custom code for handling the conversion of the raw numbers
> representing dates/timestamps but this also seems like a bad idea. The Cell
> class has getLocalDateTimeCellValue and this has the right logic for
> converting 1904 and 1900 based dates - yes, Excel uses 2 different formats.
> Code that processes excel files is a real pain to get right because the
> Microsoft storage format is really bad.
>
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