[GitHub] [drill] paul-rogers commented on issue #1749: DRILL-7177: Format Plugin for Excel Files

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paul-rogers commented on issue #1749: DRILL-7177: Format Plugin for Excel Files
URL: https://github.com/apache/drill/pull/1749#issuecomment-542792797
 
 
   One additional thought: how are column types handled? Do we require all fields to have the same types within a column?
   
   Name | Balance
   ----| -----
   Fred | 123.45
   Barney | 556.78
   
   If so, then it might make sense to hold an array of column handler objects, like in the earlier version of the Regex plugin, that holds the column accessor and performs any required type conversions. This would be cleaner/faster than doing a `switch` per column.
   
   Can a column type vary?
   
   Name | Balance
   ----| -----
   Fred | 123.45
   Barney | "Not sure"
   
   If so, then the code has to handle conversions. The above would generate an error, but would we allow:
   
   Name | Balance
   ----| -----
   Fred | 123.45
   Barney | "556.78"
   
   Can a column start as empty (null) so that we have to defer type selection?
   
   Name | Balance
   ----| -----
   Fred | 
   Barney | 556.78
   
   If so, then we need a way to defer column type selection until we see the first non-null value. The (not yet merged) new JSON reader hands the deferred-type case; I can share that logic if you need it.

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