Fixed scale column for the getColumns function to match the simba output. (#989)

## Description
<!-- Provide a brief summary of the changes made and the issue they aim
to address.-->
Fixed the DECIMAL_DIGITS column to return non zero values for timestamp,
decimal, numeric datatype. For the rest of the datatypes, the value
returned is zero.
## Testing
<!-- Describe how the changes have been tested-->
Added unit tests
## Additional Notes to the Reviewer
<!-- Share any additional context or insights that may help the reviewer
understand the changes better. This could include challenges faced,
limitations, or compromises made during the development process.
Also, mention any areas of the code that you would like the reviewer to
focus on specifically. -->
[PECOBLR-840](https://databricks.atlassian.net/browse/PECOBLR-840)
Fixes [#960](#960)



[PECOBLR-840]:
https://databricks.atlassian.net/browse/PECOBLR-840?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: msrathore-db

NEXT_CHANGELOG.md

@@ -23,6 +23,7 @@
 - Fixed volume operations not completing unless the ResultSet is fully iterated.
 - Fixed `connection.getMetadata().getColumns()` to return the correct SQL data type code for complex type columns.
 - Fixed a bug in the JDBC driver's metadata parsing for nested decimal fields within struct types.
-- Fix case sensitive table search in `connection.getMetadata().getTables()`
+- Fixed case sensitive table search in `connection.getMetadata().getTables()`
+- Fixed `connection.getMetadata().getColumns()` to return the correct scale.
 ---
 *Note: When making changes, please add your change under the appropriate section with a brief description.* 

src/main/java/com/databricks/jdbc/dbclient/impl/common/MetadataResultSetBuilder.java

@@ -2,6 +2,7 @@
 
 import static com.databricks.jdbc.common.MetadataResultConstants.*;
 import static com.databricks.jdbc.common.util.DatabricksTypeUtil.INTERVAL;
+import static com.databricks.jdbc.common.util.WildcardUtil.isNullOrEmpty;
 import static com.databricks.jdbc.dbclient.impl.common.CommandConstants.*;
 import static com.databricks.jdbc.dbclient.impl.common.TypeValConstants.*;
 
@@ -212,8 +213,13 @@ List<List<Object>> getRows(
                 } else {
                   object = "NO";
                 }
-              } else if (mappedColumn.getColumnName().equals(DECIMAL_DIGITS_COLUMN.getColumnName())
-                  || mappedColumn.getColumnName().equals(NUM_PREC_RADIX_COLUMN.getColumnName())) {
+              } else if (mappedColumn
+                  .getColumnName()
+                  .equals(DECIMAL_DIGITS_COLUMN.getColumnName())) {
+                object = getUpdatedDecimalDigits(stripBaseTypeName(typeVal), object);
+              } else if (mappedColumn
+                  .getColumnName()
+                  .equals(NUM_PREC_RADIX_COLUMN.getColumnName())) {
                 if (object == null) {
                   object = 0;
                 }
@@ -424,6 +430,37 @@ int getBufferLength(String typeVal) {
     return getSizeInBytes(sqlType);
   }
 
+  /**
+   * Overrides DECIMAL_DIGITS value for specific data types. Returns non-zero only for DECIMAL,
+   * NUMERIC, TIMESTAMP, and TIMESTAMP_NTZ.
+   *
+   * @param baseTypeVal the column type name
+   * @param scaleObject the original scale value (can be null)
+   * @return scale value for DECIMAL/NUMERIC, 9 for TIMESTAMP types, 0 otherwise
+   * @example
+   *     <pre>
+   * getUpdatedDecimalDigits("DECIMAL", 2) → 2
+   * getUpdatedDecimalDigits("TIMESTAMP", 6) → 9
+   * getUpdatedDecimalDigits("FLOAT", 7) → 0
+   * </pre>
+   */
+  int getUpdatedDecimalDigits(String baseTypeVal, Object scaleObject) {
+    if (scaleObject == null) {
+      return 0;
+    }
+    int scale = (int) scaleObject;
+    if (isNullOrEmpty(baseTypeVal)) {
+      return 0;
+    }
+    if (baseTypeVal.contains(DECIMAL_TYPE) || baseTypeVal.contains(NUMERIC_TYPE)) {
+      return scale;
+    }
+    if (baseTypeVal.contains(TIMESTAMP_TYPE) || baseTypeVal.contains(TIMESTAMP_NTZ_TYPE)) {
+      return 9;
+    }
+    return 0;
+  }
+
   /**
    * Extracts the character octet length from a given SQL type definition. For example, for input
    * "VARCHAR(100)", it returns 100. For inputs without a specified length or invalid inputs, it
@@ -891,8 +928,10 @@ List<List<Object>> getThriftRows(List<List<Object>> rows, List<ResultColumn> col
                   object = "YES";
                 }
               }
-              if (column.getColumnName().equals(DECIMAL_DIGITS_COLUMN.getColumnName())
-                  || column.getColumnName().equals(NUM_PREC_RADIX_COLUMN.getColumnName())) {
+              if (column.getColumnName().equals(DECIMAL_DIGITS_COLUMN.getColumnName())) {
+                object = getUpdatedDecimalDigits(stripBaseTypeName(typeVal), object);
+              }
+              if (column.getColumnName().equals(NUM_PREC_RADIX_COLUMN.getColumnName())) {
                 if (object == null) {
                   object = 0;
                 }

src/main/java/com/databricks/jdbc/dbclient/impl/common/TypeValConstants.java

@@ -8,6 +8,7 @@ public class TypeValConstants {
   static final String BOOLEAN_TYPE = "BOOLEAN";
   static final String DATE_TYPE = "DATE";
   static final String TIMESTAMP_TYPE = "TIMESTAMP";
+  static final String TIMESTAMP_NTZ_TYPE = "TIMESTAMP_NTZ";
   static final String DECIMAL_TYPE = "DECIMAL";
   static final String BINARY_TYPE = "BINARY";
   static final String ARRAY_TYPE = "ARRAY";

src/test/java/com/databricks/jdbc/dbclient/impl/common/MetadataResultSetBuilderTest.java

@@ -531,4 +531,66 @@ void testComplexTypesReturnActualCodesWhenSupportEnabled() throws SQLException {
     assertEquals(1111, variantRow.get(0));
     assertEquals(1111, variantRow.get(2));
   }
+
+  @Test
+  void testDecimalDigitsColumnInGetThriftRows() {
+    List<ResultColumn> columns = Arrays.asList(COLUMN_TYPE_COLUMN, DECIMAL_DIGITS_COLUMN);
+
+    List<List<Object>> rows =
+        Arrays.asList(
+            Arrays.asList("DECIMAL(10,2)", 2),
+            Arrays.asList("TIMESTAMP", 6),
+            Arrays.asList("INT", 0),
+            Arrays.asList("VARCHAR(100)", 0),
+            Arrays.asList("DECIMAL(15,5)", 5),
+            Arrays.asList("TIMESTAMP_NTZ", 6),
+            Arrays.asList("DECIMAL", 0));
+
+    List<List<Object>> updatedRows = metadataResultSetBuilder.getThriftRows(rows, columns);
+
+    assertEquals(2, updatedRows.get(0).get(1), "DECIMAL(10,2) should have scale 2");
+    assertEquals(9, updatedRows.get(1).get(1), "TIMESTAMP should have scale 9");
+    assertEquals(0, updatedRows.get(2).get(1), "INT should have scale 0");
+    assertEquals(0, updatedRows.get(3).get(1), "VARCHAR should have scale 0");
+    assertEquals(5, updatedRows.get(4).get(1), "DECIMAL(15,5) should have scale 5");
+    assertEquals(9, updatedRows.get(5).get(1), "TIMESTAMP_NTZ should have scale 9");
+    assertEquals(0, updatedRows.get(6).get(1), "DECIMAL should have scale 0");
+  }
+
+  private static Stream<Arguments> provideDecimalDigitsArguments() {
+    return Stream.of(
+        Arguments.of("DECIMAL(10,2)", 2, 2, "DECIMAL(10,2) should have scale 2"),
+        Arguments.of("TIMESTAMP", 6, 9, "TIMESTAMP should have scale 9"),
+        Arguments.of("INT", 0, 0, "INT should have scale 0"),
+        Arguments.of("VARCHAR(100)", 0, 0, "VARCHAR should have scale 0"),
+        Arguments.of("DECIMAL(15,5)", 5, 5, "DECIMAL(15,5) should have scale 5"),
+        Arguments.of("TIMESTAMP_NTZ", 6, 9, "TIMESTAMP_NTZ should have scale 9"),
+        Arguments.of("DECIMAL", 0, 0, "DECIMAL should have scale 0"));
+  }
+
+  @ParameterizedTest
+  @MethodSource("provideDecimalDigitsArguments")
+  void testDecimalDigitsColumnInGetRows(
+      String typeName, int inputScale, int expectedScale, String message) throws SQLException {
+    DatabricksResultSet resultSet = mock(DatabricksResultSet.class);
+    when(resultSet.next()).thenReturn(true).thenReturn(false);
+
+    for (ResultColumn resultColumn : COLUMN_COLUMNS) {
+      if (resultColumn.getResultSetColumnName().equals("SQLDataType")) {
+        // Special handling begins from SQLDataType columns onward; getObject is no longer invoked.
+        break;
+      }
+      when(resultSet.getObject(resultColumn.getResultSetColumnName())).thenReturn(null);
+    }
+    when(resultSet.getObject(IS_NULLABLE_COLUMN.getResultSetColumnName())).thenReturn("true");
+    when(resultSet.getString(COLUMN_TYPE_COLUMN.getResultSetColumnName())).thenReturn(typeName);
+    when(resultSet.getObject(DECIMAL_DIGITS_COLUMN.getResultSetColumnName()))
+        .thenReturn(inputScale);
+
+    List<List<Object>> rows =
+        metadataResultSetBuilder.getRows(
+            resultSet, COLUMN_COLUMNS, new DefaultDatabricksResultSetAdapter());
+
+    assertEquals(expectedScale, rows.get(0).get(8), message);
+  }
 }