[SPARK-47300][SQL] quoteIfNeeded should quote identifier starts with digits

sql/api/src/main/scala/org/apache/spark/sql/catalyst/util/QuotingUtils.scala

@@ -16,6 +16,8 @@
  */
 package org.apache.spark.sql.catalyst.util
 
+import java.util.regex.Pattern
+
 import org.apache.spark.sql.connector.catalog.Identifier
 
 object QuotingUtils {
@@ -41,11 +43,13 @@ object QuotingUtils {
     name.map(part => quoteIdentifier(part)).mkString(".")
   }
 
+  private val validIdentPattern = Pattern.compile("^[a-zA-Z_][a-zA-Z0-9_]*")
+
   def quoteIfNeeded(part: String): String = {
-    if (part.matches("[a-zA-Z0-9_]+") && !part.matches("\\d+")) {
+    if (validIdentPattern.matcher(part).matches()) {
       part
     } else {
-      s"`${part.replace("`", "``")}`"
+      quoteIdentifier(part)
     }
   }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/QuotingUtilsSuite.scala

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.util
+
+import org.apache.spark.SparkFunSuite
+
+class QuotingUtilsSuite extends SparkFunSuite {
+
+  test("do not quote for legal identifier strings") {
+    assert(quoteIfNeeded("a") == "a")
+    assert(quoteIfNeeded("a0") == "a0")
+    assert(quoteIfNeeded("a0a") == "a0a")
+    assert(quoteIfNeeded("_") == "_")
+    assert(quoteIfNeeded("_a") == "_a")
+    assert(quoteIfNeeded("_0") == "_0")
+    assert(quoteIfNeeded("_ab_") === "_ab_")
+  }
+
+  test("quote for illegal identifier strings") {
+    assert(quoteIfNeeded("&") == "`&`")
+    assert(quoteIfNeeded("a b") === "`a b`")
+    assert(quoteIfNeeded("a*b") === "`a*b`")
+    assert(quoteIfNeeded("0") == "`0`")
+    assert(quoteIfNeeded("01") == "`01`")
+    assert(quoteIfNeeded("0d") == "`0d`")
+    assert(quoteIfNeeded("") === "``")
+  }
+}

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/StringUtilsSuite.scala

@@ -129,16 +129,6 @@ class StringUtilsSuite extends SparkFunSuite with SQLHelper {
     }
   }
 
-  test("SPARK-34872: quoteIfNeeded should quote a string which contains non-word characters") {
-    assert(quoteIfNeeded("a b") === "`a b`")
-    assert(quoteIfNeeded("a*b") === "`a*b`")
-    assert(quoteIfNeeded("123") === "`123`")
-    assert(quoteIfNeeded("1a") === "1a")
-    assert(quoteIfNeeded("_ab_") === "_ab_")
-    assert(quoteIfNeeded("_") === "_")
-    assert(quoteIfNeeded("") === "``")
-  }
-
   test("SPARK-43841: mix of multipart and single-part identifiers") {
     val baseString = "b"
     // mix of multipart and single-part