gianm commented on code in PR #12770:
URL: https://github.com/apache/druid/pull/12770#discussion_r918569327
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sql/src/main/java/org/apache/druid/sql/calcite/external/ExternalTableMacro.java:
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@@ -59,6 +63,21 @@ public TranslatableTable apply(final List<Object> arguments)
final InputFormat inputFormat = jsonMapper.readValue((String)
arguments.get(1), InputFormat.class);
final RowSignature signature = jsonMapper.readValue((String)
arguments.get(2), RowSignature.class);
+ // Prevent a RowSignature that has a ColumnSignature with name "__time"
and type that is not LONG because it will most
+ // likely be used in a Calcite function, and cause an exception.
+ // Columns with name __time are automatically assumed to be of the type
SqlTypeName.TIMESTAMP because of the logic
+ // present in RowSignatures#toRelDataType
+ // This is not the most optimal approach because of the following
caveats:
+ // 1. __time in the external data source may map to a different column
+ // 2. __time in the external data source might be ignored while
ingesting the data
+ // 3. Even if __time is of type LONG, it may be used with some function,
which would cause the abovementioned Calcite failure
+ // The most optimal solution would be to prevent assumption of the
__time column having the type SqlTypeName.TIMESTAMP
Review Comment:
Thanks for looking into this!
Is there a reason why we cannot do the more optimal solution now? Something
like: for `__time`, have RowSignatures.toRelDataType return TIMESTAMP for
regular Druid tables, and the type from the provided signature otherwise. To
get the information through, we could add a parameter to toRelDataType like
`boolean isDruidTable`.
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