[SPARK-15557][SQL] cast the string into DoubleType when it's used together with decimal

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala

@@ -290,11 +290,6 @@ object TypeCoercion {
       // Skip nodes who's children have not been resolved yet.
       case e if !e.childrenResolved => e
 
-      case a @ BinaryArithmetic(left @ StringType(), right @ DecimalType.Expression(_, _)) =>
-        a.makeCopy(Array(Cast(left, DecimalType.SYSTEM_DEFAULT), right))
-      case a @ BinaryArithmetic(left @ DecimalType.Expression(_, _), right @ StringType()) =>
-        a.makeCopy(Array(left, Cast(right, DecimalType.SYSTEM_DEFAULT)))
-
       case a @ BinaryArithmetic(left @ StringType(), right) =>
         a.makeCopy(Array(Cast(left, DoubleType), right))
       case a @ BinaryArithmetic(left, right @ StringType()) =>

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisSuite.scala

@@ -182,8 +182,7 @@ class AnalysisSuite extends AnalysisTest {
     assert(pl(0).dataType == DoubleType)
     assert(pl(1).dataType == DoubleType)
     assert(pl(2).dataType == DoubleType)
-    // StringType will be promoted into Decimal(38, 18)
-    assert(pl(3).dataType == DecimalType(38, 22))
+    assert(pl(3).dataType == DoubleType)
     assert(pl(4).dataType == DoubleType)
   }
 

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/json/JsonSuite.scala

@@ -446,13 +446,13 @@ class JsonSuite extends QueryTest with SharedSQLContext with TestJsonData {
     // Number and String conflict: resolve the type as number in this query.
     checkAnswer(
       sql("select num_str + 1.2 from jsonTable where num_str > 14"),
-      Row(BigDecimal("92233720368547758071.2"))
+      Row(92233720368547758071.2)
     )
 
     // Number and String conflict: resolve the type as number in this query.
     checkAnswer(
       sql("select num_str + 1.2 from jsonTable where num_str >= 92233720368547758060"),
-      Row(new java.math.BigDecimal("92233720368547758071.2"))
+      Row(new java.math.BigDecimal("92233720368547758071.2").doubleValue)
     )
 
     // String and Boolean conflict: resolve the type as string.

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

@@ -1560,4 +1560,23 @@ class SQLQuerySuite extends QueryTest with SQLTestUtils with TestHiveSingleton {
       checkAnswer(sql("SELECT * FROM tbl"), Row(1, "a"))
     }
   }
+
+  test("spark-15557 promote string test") {
+    withTable("tbl") {
+      sql("CREATE TABLE tbl(c1 string, c2 string)")
+      sql("insert into tbl values ('3', '2.3')")
+      checkAnswer(
+        sql("select (cast (99 as decimal(19,6)) + cast('3' as decimal)) * cast('2.3' as decimal)"),
+        Row(204.0)
+      )
+      checkAnswer(
+        sql("select (cast(99 as decimal(19,6)) + '3') *'2.3' from tbl"),
+        Row(234.6)
+      )
+      checkAnswer(
+        sql("select (cast(99 as decimal(19,6)) + c1) * c2 from tbl"),
+        Row(234.6)
+      )
+    }
+  }
 }