[SPARK-9281] [SQL] use decimal or double when parsing SQL

Right now, we use double to parse all the float number in SQL. When it's used in expression together with DecimalType, it will turn the decimal into double as well. Also it will loss some precision when using double.

This PR change to parse float number to decimal or double, based on it's  using scientific notation or not, see https://msdn.microsoft.com/en-us/library/ms179899.aspx

This is a break change, should we doc it somewhere?

Author: Davies Liu <davies@databricks.com>

Closes #7642 from davies/parse_decimal and squashes the following commits:

1f576d9 [Davies Liu] Merge branch 'master' of github.com:apache/spark into parse_decimal
5e142b6 [Davies Liu] fix scala style
eca99de [Davies Liu] fix tests
2afe702 [Davies Liu] Merge branch 'master' of github.com:apache/spark into parse_decimal
f4a320b [Davies Liu] Update SqlParser.scala
1c48e34 [Davies Liu] use decimal or double when parsing SQL

1 files changed, 2 insertions, 2 deletions

diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisSuite.scala
index 4589facb49..221b4e92f0 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisSuite.scala
@@ -145,11 +145,11 @@ class AnalysisSuite extends AnalysisTest {
         'e / 'e as 'div5))
     val pl = plan.asInstanceOf[Project].projectList
 
-    // StringType will be promoted into Double
     assert(pl(0).dataType == DoubleType)
     assert(pl(1).dataType == DoubleType)
     assert(pl(2).dataType == DoubleType)
-    assert(pl(3).dataType == DoubleType)
+    // StringType will be promoted into Decimal(38, 18)
+    assert(pl(3).dataType == DecimalType(38, 29))
     assert(pl(4).dataType == DoubleType)
   }