[GitHub] [spark] HyukjinKwon commented on a change in pull request #30479: [SPARK-33527][SQL] Extend the function of decode so as consistent with mainstream databases

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

HyukjinKwon commented on a change in pull request #30479:
URL: https://github.com/apache/spark/pull/30479#discussion_r539120389



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringExpressions.scala
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@@ -2082,6 +2083,65 @@ case class UnBase64(child: Expression)
   }
 }
 
+object Decode {
+  def createExpr(params: Seq[Expression]): Expression = {
+    params.length match {
+      case 0 | 1 =>
+        throw new AnalysisException("Invalid number of arguments for function decode. " +
+          s"Expected: 2; Found: ${params.length}")
+      case 2 => StringDecode(params.head, params.last)
+      case _ =>
+        val input = params.head
+        val other = params.tail
+        val itr = other.iterator
+        var default: Expression = Literal.create(null, StringType)
+        val branches = ArrayBuffer.empty[(Expression, Expression)]
+        while (itr.hasNext) {
+          val search = itr.next
+          if (itr.hasNext) {
+            val condition = EqualTo(input, search)
+            branches += ((condition, itr.next))
+          } else {
+            default = search
+          }
+        }
+        CaseWhen(branches.seq, default)
+    }
+  }
+}
+
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+  usage = """
+            |_FUNC_(bin, charset) - Decodes the first argument using the second argument character set.
+            |
+            |_FUNC_(expr, search, result [, search, result ] ... [, default]) - Decode compares expr
+            |  to each search value one by one. If expr is equal to a search, returns the corresponding result.
+            |  If no match is found, then Oracle returns default. If default is omitted, returns null.
+          """,
+  examples = """
+    Examples:
+      > SELECT _FUNC_(encode('abc', 'utf-8'), 'utf-8');
+       abc
+      > SELECT _FUNC_(2, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle', 'Non domestic');
+       San Francisco
+      > SELECT _FUNC_(6, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle', 'Non domestic');
+       Non domestic
+      > SELECT _FUNC_(6, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle');
+       NULL
+  """,
+  since = "3.1.0")

Review comment:
       BTW, new feature should arrive in 3.2.0 because branch-3.1 is out now.




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