[SPARK-20341][SQL] Support BigInt's value that does not fit in long value range

sql/catalyst/src/main/scala/org/apache/spark/sql/types/Decimal.scala

@@ -132,14 +132,22 @@ final class Decimal extends Ordered[Decimal] with Serializable {
   }
 
   /**
-   * Set this Decimal to the given BigInteger value. Will have precision 38 and scale 0.
+   * If the value is not in the range of long, convert it to BigDecimal and
+   * the precision and scale are based on the converted value.
+   *
+   * This code avoids BigDecimal object allocation as possible to improve runtime efficiency
    */
   def set(bigintval: BigInteger): Decimal = {
-    this.decimalVal = null
-    this.longVal = bigintval.longValueExact()
-    this._precision = DecimalType.MAX_PRECISION
-    this._scale = 0
-    this
+    try {
+      this.decimalVal = null
+      this.longVal = bigintval.longValueExact()
+      this._precision = DecimalType.MAX_PRECISION
+      this._scale = 0
+      this
+    } catch {
+      case _: ArithmeticException =>
+        set(BigDecimal(bigintval))
+    }
   }
 
   /**

sql/catalyst/src/test/scala/org/apache/spark/sql/types/DecimalSuite.scala

@@ -212,4 +212,10 @@ class DecimalSuite extends SparkFunSuite with PrivateMethodTester {
       }
     }
   }
+
+  test("SPARK-20341: support BigInt's value does not fit in long value range") {
+    val bigInt = scala.math.BigInt("9223372036854775808")
+    val decimal = Decimal.apply(bigInt)
+    assert(decimal.toJavaBigDecimal.unscaledValue.toString === "9223372036854775808")
+  }
 }