[SPARK-17832][SQL] TableIdentifier.quotedString creates un-parseable names when name contains a backtick

## What changes were proposed in this pull request?

The `quotedString` method in `TableIdentifier` and `FunctionIdentifier` produce an illegal (un-parseable) name when the name contains a backtick. For example:
```
import org.apache.spark.sql.catalyst.parser.CatalystSqlParser._
import org.apache.spark.sql.catalyst.TableIdentifier
import org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute
val complexName = TableIdentifier("`weird`table`name", Some("`d`b`1"))
parseTableIdentifier(complexName.unquotedString) // Does not work
parseTableIdentifier(complexName.quotedString) // Does not work
parseExpression(complexName.unquotedString) // Does not work
parseExpression(complexName.quotedString) // Does not work
```
We should handle the backtick properly to make `quotedString` parseable.

## How was this patch tested?
Add new testcases in `TableIdentifierParserSuite` and `ExpressionParserSuite`.

Author: jiangxingbo <jiangxb1987@gmail.com>

Closes #15403 from jiangxb1987/backtick.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/identifiers.scala

@@ -17,7 +17,6 @@
 
 package org.apache.spark.sql.catalyst
 
-
 /**
  * An identifier that optionally specifies a database.
  *
@@ -29,8 +28,16 @@ sealed trait IdentifierWithDatabase {
 
   def database: Option[String]
 
+  /*
+   * Escapes back-ticks within the identifier name with double-back-ticks.
+   */
+  private def quoteIdentifier(name: String): String = name.replace("`", "``")
+
   def quotedString: String = {
-    if (database.isDefined) s"`${database.get}`.`$identifier`" else s"`$identifier`"
+    val replacedId = quoteIdentifier(identifier)
+    val replacedDb = database.map(quoteIdentifier(_))
+
+    if (replacedDb.isDefined) s"`${replacedDb.get}`.`$replacedId`" else s"`$replacedId`"
   }
 
   def unquotedString: String = {

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/ExpressionParserSuite.scala

@@ -18,7 +18,7 @@ package org.apache.spark.sql.catalyst.parser
 
 import java.sql.{Date, Timestamp}
 
-import org.apache.spark.sql.catalyst.{FunctionIdentifier, TableIdentifier}
+import org.apache.spark.sql.catalyst.FunctionIdentifier
 import org.apache.spark.sql.catalyst.analysis.{UnresolvedAttribute, _}
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.PlanTest
@@ -535,4 +535,13 @@ class ExpressionParserSuite extends PlanTest {
     // ".123BD" should not be treated as token of type BIGDECIMAL_LITERAL
     assertEqual("a.123BD_column", UnresolvedAttribute("a.123BD_column"))
   }
+
+  test("SPARK-17832 function identifier contains backtick") {
+    val complexName = FunctionIdentifier("`ba`r", Some("`fo`o"))
+    assertEqual(complexName.quotedString, UnresolvedAttribute("`fo`o.`ba`r"))
+    intercept(complexName.unquotedString, "mismatched input")
+    // Function identifier contains countious backticks should be treated correctly.
+    val complexName2 = FunctionIdentifier("ba``r", Some("fo``o"))
+    assertEqual(complexName2.quotedString, UnresolvedAttribute("fo``o.ba``r"))
+  }
 }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/TableIdentifierParserSuite.scala

@@ -104,4 +104,14 @@ class TableIdentifierParserSuite extends SparkFunSuite {
     // ".123BD" should not be treated as token of type BIGDECIMAL_LITERAL
     assert(parseTableIdentifier("a.123BD_LIST") == TableIdentifier("123BD_LIST", Some("a")))
   }
+
+  test("SPARK-17832 table identifier - contains backtick") {
+    val complexName = TableIdentifier("`weird`table`name", Some("`d`b`1"))
+    assert(complexName === parseTableIdentifier("```d``b``1`.```weird``table``name`"))
+    assert(complexName === parseTableIdentifier(complexName.quotedString))
+    intercept[ParseException](parseTableIdentifier(complexName.unquotedString))
+    // Table identifier contains countious backticks should be treated correctly.
+    val complexName2 = TableIdentifier("x``y", Some("d``b"))
+    assert(complexName2 === parseTableIdentifier(complexName2.quotedString))
+  }
 }