[GitHub] [spark] cloud-fan commented on a diff in pull request #36365: [SPARK-28516][SQL] Implement `to_char` and `try_to_char` functions to format Decimal values as strings

[GitBox <gi...@apache.org>]

cloud-fan commented on code in PR #36365:
URL: https://github.com/apache/spark/pull/36365#discussion_r868281343


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/numberFormatExpressions.scala:
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@@ -168,3 +168,157 @@ case class TryToNumber(left: Expression, right: Expression)
       newRight: Expression): TryToNumber =
     copy(left = newLeft, right = newRight)
 }
+
+/**
+ * A function that converts decimal values to strings, returning NULL if the decimal value fails to
+ * match the format string.
+ */
+@ExpressionDescription(
+  usage = """
+    _FUNC_(numberExpr, formatExpr) - Convert `numberExpr` to a string based on the `formatExpr`.
+      Throws an exception if the conversion fails. The format can consist of the following
+      characters, case insensitive:
+        '0' or '9': Specifies an expected digit between 0 and 9. A sequence of 0 or 9 in the format
+          string matches a sequence of digits in the input value, generating a result string of the
+          same length as the corresponding sequence in the format string. The result string is
+          left-padded with zeros if the 0/9 sequence comprises more digits than the matching part of
+          the decimal value, starts with 0, and is before the decimal point.

Review Comment:
   shall we mention that it's left-padded with spaces otherwise?



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