[SPARK-28152][SQL][2.4] Mapped ShortType to SMALLINT and FloatType to REAL for MsSqlServerDialect

## What changes were proposed in this pull request?
This is a backport of SPARK-28152 to Spark 2.4.

SPARK-28152 PR aims to correct mappings in `MsSqlServerDialect`. `ShortType` is mapped to `SMALLINT` and `FloatType` is mapped to `REAL` per [JBDC mapping]( https://docs.microsoft.com/en-us/sql/connect/jdbc/using-basic-data-types?view=sql-server-2017) respectively.

ShortType and FloatTypes are not correctly mapped to right JDBC types when using JDBC connector. This results in tables and spark data frame being created with unintended types. The issue was observed when validating against SQLServer.

Refer [JBDC mapping]( https://docs.microsoft.com/en-us/sql/connect/jdbc/using-basic-data-types?view=sql-server-2017  ) for guidance on mappings between SQLServer, JDBC and Java. Note that java "Short" type should be mapped to JDBC "SMALLINT" and java Float should be mapped to JDBC "REAL".

Some example issue that can happen because of wrong mappings
    - Write from df with column type results in a SQL table of with column type as INTEGER as opposed to SMALLINT.Thus a larger table that expected.
    - Read results in a dataframe with type INTEGER as opposed to ShortType

- ShortType has a problem in both the the write and read path
- FloatTypes only have an issue with read path. In the write path Spark data type 'FloatType' is correctly mapped to JDBC equivalent data type 'Real'. But in the read path when JDBC data types need to be converted to Catalyst data types ( getCatalystType) 'Real' gets incorrectly gets mapped to 'DoubleType' rather than 'FloatType'.

Refer apache#28151 which contained this fix as one part of a larger PR.  Following PR apache#28151 discussion it was decided to file seperate PRs for each of the fixes.

## How was this patch tested?
UnitTest added in JDBCSuite.scala and these were tested.
Integration test updated and passed in MsSqlServerDialect.scala
E2E test done with SQLServer

Closes apache#25248 from shivsood/PR_28152_2.4.

Authored-by: shivsood <shivsood@microsoft.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

Author: shivsood

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

@@ -120,24 +120,24 @@ class MsSqlServerIntegrationSuite extends DockerJDBCIntegrationSuite {
     assert(types.length == 12)
     assert(types(0).equals("class java.lang.Boolean"))
     assert(types(1).equals("class java.lang.Integer"))
-    assert(types(2).equals("class java.lang.Integer"))
+    assert(types(2).equals("class java.lang.Short"))
     assert(types(3).equals("class java.lang.Integer"))
     assert(types(4).equals("class java.lang.Long"))
     assert(types(5).equals("class java.lang.Double"))
-    assert(types(6).equals("class java.lang.Double"))
-    assert(types(7).equals("class java.lang.Double"))
+    assert(types(6).equals("class java.lang.Float"))
+    assert(types(7).equals("class java.lang.Float"))
     assert(types(8).equals("class java.math.BigDecimal"))
     assert(types(9).equals("class java.math.BigDecimal"))
     assert(types(10).equals("class java.math.BigDecimal"))
     assert(types(11).equals("class java.math.BigDecimal"))
     assert(row.getBoolean(0) == false)
     assert(row.getInt(1) == 255)
-    assert(row.getInt(2) == 32767)
+    assert(row.getShort(2) == 32767)
     assert(row.getInt(3) == 2147483647)
     assert(row.getLong(4) == 9223372036854775807L)
     assert(row.getDouble(5) == 1.2345678901234512E14) // float = float(53) has 15-digits precision
-    assert(row.getDouble(6) == 1.23456788103168E14)   // float(24) has 7-digits precision
-    assert(row.getDouble(7) == 1.23456788103168E14)   // real = float(24)
+    assert(row.getFloat(6) == 1.23456788103168E14)   // float(24) has 7-digits precision
+    assert(row.getFloat(7) == 1.23456788103168E14)   // real = float(24)
     assert(row.getAs[BigDecimal](8).equals(new BigDecimal("123.00")))
     assert(row.getAs[BigDecimal](9).equals(new BigDecimal("12345.12000")))
     assert(row.getAs[BigDecimal](10).equals(new BigDecimal("922337203685477.5800")))

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

@@ -30,7 +30,11 @@ private object MsSqlServerDialect extends JdbcDialect {
       // String is recommend by Microsoft SQL Server for datetimeoffset types in non-MS clients
       Option(StringType)
     } else {
-      None
+      sqlType match {
+        case java.sql.Types.SMALLINT => Some(ShortType)
+        case java.sql.Types.REAL => Some(FloatType)
+        case _ => None
+      }
     }
   }
 
@@ -39,6 +43,7 @@ private object MsSqlServerDialect extends JdbcDialect {
     case StringType => Some(JdbcType("NVARCHAR(MAX)", java.sql.Types.NVARCHAR))
     case BooleanType => Some(JdbcType("BIT", java.sql.Types.BIT))
     case BinaryType => Some(JdbcType("VARBINARY(MAX)", java.sql.Types.VARBINARY))
+    case ShortType => Some(JdbcType("SMALLINT", java.sql.Types.SMALLINT))
     case _ => None
   }
 

sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala

@@ -870,6 +870,17 @@ class JDBCSuite extends QueryTest
       "BIT")
     assert(msSqlServerDialect.getJDBCType(BinaryType).map(_.databaseTypeDefinition).get ==
       "VARBINARY(MAX)")
+    assert(msSqlServerDialect.getJDBCType(ShortType).map(_.databaseTypeDefinition).get ==
+      "SMALLINT")
+  }
+
+  test("SPARK-28152 MsSqlServerDialect catalyst type mapping") {
+    val msSqlServerDialect = JdbcDialects.get("jdbc:sqlserver")
+    val metadata = new MetadataBuilder().putLong("scale", 1)
+    assert(msSqlServerDialect.getCatalystType(java.sql.Types.SMALLINT, "SMALLINT", 1,
+      metadata).get == ShortType)
+    assert(msSqlServerDialect.getCatalystType(java.sql.Types.REAL, "REAL", 1,
+      metadata).get == FloatType)
   }
 
   test("table exists query by jdbc dialect") {