NobiGo commented on code in PR #3817:
URL: https://github.com/apache/calcite/pull/3817#discussion_r1639121901
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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:
> 1. SELECT NULL UNION ALL SELECT NULL
this is intentional to make sure when the subquery include more then one
value ,This SQL will throw exception.
2: Suggestion: Use COUNT(field) instead of COUNT(*)
Please check CALCITE-6430.
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