mihaibudiu commented on code in PR #3817:
URL: https://github.com/apache/calcite/pull/3817#discussion_r1640155876
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core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java:
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@@ -93,6 +101,41 @@ public static void unparseSparkArrayAndMap(SqlWriter writer,
writer.endList(frame);
}
+
+ /**
+ * Rewrite SINGLE_VALUE use SparkSQL Mode.
+ *
+ * <blockquote><pre>
+ * CASE COUNT(*)
+ * WHEN 0 THEN NULL
+ * WHEN 1 THEN MIN(<result>)
+ * ELSE (SELECT NULL UNION ALL SELECT NULL))
Review Comment:
You should add a comment in the code about the UNION ALL. Your intent is not
obvious at all.
I am not sure how the runtime error will look; if the error will mention a
UNION ALL operator, the users may be confused, since there is no UNION ALL in
the original query, but I guess there isn't much you can do about this.
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