[SPARK-8052] [SQL] Use java.math.BigDecimal for casting String to Dec…

…imal instead of using toDouble

JIRA: https://issues.apache.org/jira/browse/SPARK-8052

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes apache#6645 from viirya/cast_string_integraltype and squashes the following commits:

e19c6a3 [Liang-Chi Hsieh] For comment.
c3e472a [Liang-Chi Hsieh] Add test.
7ced9b0 [Liang-Chi Hsieh] Use java.math.BigDecimal for casting String to Decimal instead of using toDouble.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala

@@ -17,6 +17,7 @@
 
 package org.apache.spark.sql.catalyst.expressions
 
+import java.math.{BigDecimal => JavaBigDecimal}
 import java.sql.{Date, Timestamp}
 import java.text.{DateFormat, SimpleDateFormat}
 
@@ -320,7 +321,7 @@ case class Cast(child: Expression, dataType: DataType) extends UnaryExpression w
   private[this] def castToDecimal(from: DataType, target: DecimalType): Any => Any = from match {
     case StringType =>
       buildCast[UTF8String](_, s => try {
-        changePrecision(Decimal(s.toString.toDouble), target)
+        changePrecision(Decimal(new JavaBigDecimal(s.toString)), target)
       } catch {
         case _: NumberFormatException => null
       })

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala

@@ -875,6 +875,10 @@ class SQLQuerySuite extends QueryTest {
     }
   }
 
+  test("Cast STRING to BIGINT") {
+    checkAnswer(sql("SELECT CAST('775983671874188101' as BIGINT)"), Row(775983671874188101L))
+  }
+
   // `Math.exp(1.0)` has different result for different jdk version, so not use createQueryTest
   test("udf_java_method") {
     checkAnswer(sql(