[SPARK-20555][SQL] Fix mapping of Oracle DECIMAL types to Spark types in read path

## What changes were proposed in this pull request?

This PR is to revert some code changes in the read path of #14377. The original fix is #17830

When merging this PR, please give the credit to gaborfeher

## How was this patch tested?

Added a test case to OracleIntegrationSuite.scala

Author: Gabor Feher <[email protected]>
Author: gatorsmile <[email protected]>

Closes #18408 from gatorsmile/OracleType.

Author: Gabor Feher

external/docker-integration-tests/src/test/scala/org/apache/spark/sql/jdbc/OracleIntegrationSuite.scala

@@ -19,6 +19,7 @@ package org.apache.spark.sql.jdbc
 
 import java.sql.{Connection, Date, Timestamp}
 import java.util.Properties
+import java.math.BigDecimal
 
 import org.apache.spark.sql.Row
 import org.apache.spark.sql.test.SharedSQLContext
@@ -93,8 +94,31 @@ class OracleIntegrationSuite extends DockerJDBCIntegrationSuite with SharedSQLCo
         |USING org.apache.spark.sql.jdbc
         |OPTIONS (url '$jdbcUrl', dbTable 'datetime1', oracle.jdbc.mapDateToTimestamp 'false')
       """.stripMargin.replaceAll("\n", " "))
+
+
+    conn.prepareStatement("CREATE TABLE numerics (b DECIMAL(1), f DECIMAL(3, 2), i DECIMAL(10))").executeUpdate();
+    conn.prepareStatement(
+      "INSERT INTO numerics VALUES (4, 1.23, 9999999999)").executeUpdate();
+    conn.commit();
   }
 
+
+  test("SPARK-16625 : Importing Oracle numeric types") { 
+    val df = sqlContext.read.jdbc(jdbcUrl, "numerics", new Properties);
+    val rows = df.collect()
+    assert(rows.size == 1)
+    val row = rows(0)
+    // The main point of the below assertions is not to make sure that these Oracle types are
+    // mapped to decimal types, but to make sure that the returned values are correct.
+    // A value > 1 from DECIMAL(1) is correct:
+    assert(row.getDecimal(0).compareTo(BigDecimal.valueOf(4)) == 0)
+    // A value with fractions from DECIMAL(3, 2) is correct:
+    assert(row.getDecimal(1).compareTo(BigDecimal.valueOf(1.23)) == 0)
+    // A value > Int.MaxValue from DECIMAL(10) is correct:
+    assert(row.getDecimal(2).compareTo(BigDecimal.valueOf(9999999999l)) == 0)
+  }
+
+
   test("SPARK-12941: String datatypes to be mapped to Varchar in Oracle") {
     // create a sample dataframe with string type
     val df1 = sparkContext.parallelize(Seq(("foo"))).toDF("x")
@@ -154,27 +178,28 @@ class OracleIntegrationSuite extends DockerJDBCIntegrationSuite with SharedSQLCo
     val dfRead = spark.read.jdbc(jdbcUrl, tableName, props)
     val rows = dfRead.collect()
     // verify the data type is inserted
-    val types = rows(0).toSeq.map(x => x.getClass.toString)
-    assert(types(0).equals("class java.lang.Boolean"))
-    assert(types(1).equals("class java.lang.Integer"))
-    assert(types(2).equals("class java.lang.Long"))
-    assert(types(3).equals("class java.lang.Float"))
-    assert(types(4).equals("class java.lang.Float"))
-    assert(types(5).equals("class java.lang.Integer"))
-    assert(types(6).equals("class java.lang.Integer"))
-    assert(types(7).equals("class java.lang.String"))
-    assert(types(8).equals("class [B"))
-    assert(types(9).equals("class java.sql.Date"))
-    assert(types(10).equals("class java.sql.Timestamp"))
+    val types = dfRead.schema.map(field => field.dataType)
+    assert(types(0).equals(DecimalType(1, 0)))
+    assert(types(1).equals(DecimalType(10, 0)))
+    assert(types(2).equals(DecimalType(19, 0)))
+    assert(types(3).equals(DecimalType(19, 4)))
+    assert(types(4).equals(DecimalType(19, 4)))
+    assert(types(5).equals(DecimalType(3, 0)))
+    assert(types(6).equals(DecimalType(5, 0)))
+    assert(types(7).equals(StringType))
+    assert(types(8).equals(BinaryType))
+    assert(types(9).equals(DateType))
+    assert(types(10).equals(TimestampType))
+
     // verify the value is the inserted correct or not
     val values = rows(0)
-    assert(values.getBoolean(0).equals(booleanVal))
-    assert(values.getInt(1).equals(integerVal))
-    assert(values.getLong(2).equals(longVal))
-    assert(values.getFloat(3).equals(floatVal))
-    assert(values.getFloat(4).equals(doubleVal.toFloat))
-    assert(values.getInt(5).equals(byteVal.toInt))
-    assert(values.getInt(6).equals(shortVal.toInt))
+    assert(values.getDecimal(0).compareTo(BigDecimal.valueOf(1)) == 0)
+    assert(values.getDecimal(1).compareTo(BigDecimal.valueOf(integerVal)) == 0)
+    assert(values.getDecimal(2).compareTo(BigDecimal.valueOf(longVal)) == 0)
+    assert(values.getDecimal(3).compareTo(BigDecimal.valueOf(floatVal)) == 0)
+    assert(values.getDecimal(4).compareTo(BigDecimal.valueOf(doubleVal)) == 0)
+    assert(values.getDecimal(5).compareTo(BigDecimal.valueOf(byteVal)) == 0)
+    assert(values.getDecimal(6).compareTo(BigDecimal.valueOf(shortVal)) == 0)
     assert(values.getString(7).equals(stringVal))
     assert(values.getAs[Array[Byte]](8).mkString.equals("678"))
     assert(values.getDate(9).equals(dateVal))
@@ -183,7 +208,7 @@ class OracleIntegrationSuite extends DockerJDBCIntegrationSuite with SharedSQLCo
 
   test("SPARK-19318: connection property keys should be case-sensitive") {
     def checkRow(row: Row): Unit = {
-      assert(row.getInt(0) == 1)
+      assert(row.getDecimal(0).equals(BigDecimal.valueOf(1)))
       assert(row.getDate(1).equals(Date.valueOf("1991-11-09")))
       assert(row.getTimestamp(2).equals(Timestamp.valueOf("1996-01-01 01:23:45")))
     }

sql/core/src/main/scala/org/apache/spark/sql/jdbc/OracleDialect.scala

@@ -43,10 +43,6 @@ private case object OracleDialect extends JdbcDialect {
         // Not sure if there is a more robust way to identify the field as a float (or other
         // numeric types that do not specify a scale.
         case _ if scale == -127L => Option(DecimalType(DecimalType.MAX_PRECISION, 10))
-        case 1 => Option(BooleanType)
-        case 3 | 5 | 10 => Option(IntegerType)
-        case 19 if scale == 0L => Option(LongType)
-        case 19 if scale == 4L => Option(FloatType)
         case _ => None
       }
     } else {