[GitHub] [druid] imply-cheddar commented on a diff in pull request #14262: fix segment metadata queries for auto ingested columns that had all null values

["imply-cheddar (via GitHub)" <gi...@apache.org>]

imply-cheddar commented on code in PR #14262:
URL: https://github.com/apache/druid/pull/14262#discussion_r1191771042


##########
processing/src/main/java/org/apache/druid/segment/AutoTypeColumnIndexer.java:
##########
@@ -282,6 +282,10 @@ public ColumnCapabilities getColumnCapabilities()
 
   private ColumnType getLogicalType()
   {
+    if (fieldIndexers.isEmpty()) {
+      // we didn't see anything, so we can be anything, so why not a string?
+      return ColumnType.STRING;

Review Comment:
   Stream of conciousness: I wonder if we need a `ColumnType.NULL` to indicate something that can become anything else, but will always be null?



##########
processing/src/test/java/org/apache/druid/segment/TestHelper.java:
##########
@@ -484,6 +484,17 @@ public static Map<String, Object> makeMap(boolean explicitNulls, Object... vals)
     return theVals;
   }
 
+  public static Map<String, Object> makeMapWithExplicitNull(Object... vals)

Review Comment:
   My guess: the JVM doesn't like to statically put `null` into an Object[].  You can try, perhaps calling `makeMap(true, new Object[]{1234L, "x", null}...)`
   
   Or this is fine too.



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