diff --git a/src/MySql/AuditDiff.php b/src/MySql/AuditDiff.php
index 5085ebe..5c5f958 100755
--- a/src/MySql/AuditDiff.php
+++ b/src/MySql/AuditDiff.php
@@ -22,7 +22,7 @@ class AuditDiff
   /**
    * The metadata (additional) audit columns (as stored in the config file).
    *
-   * @var TableColumnsMetadata
+   * @var array[]
    */
   private $auditColumnsMetadata;
 
@@ -181,7 +181,7 @@ private function getDiff()
           $this->diffColumns[$table['table_name']] = new AuditDiffTable($this->config['database']['data_schema'],
                                                                         $this->config['database']['audit_schema'],
                                                                         $table['table_name'],
-                                                                        $this->config['audit_columns'],
+                                                                        $this->auditColumnsMetadata,
                                                                         $this->configMetadata[$table['table_name']]);
         }
       }
@@ -237,7 +237,7 @@ private function printDiff()
           $rows = new DiffTableHelper($this->config['database']['data_schema'],
                                       $this->config['database']['audit_schema'],
                                       $tableName,
-                                      $this->config['audit_columns'],
+                                      $this->auditColumnsMetadata,
                                       $this->full);
           $rows->appendRows($columns);
           $rows->addHighlighting();
@@ -306,6 +306,11 @@ private function resolveCanonicalAuditColumns()
       foreach ($this->config['audit_columns'] as $audit_column)
       {
         $key = StaticDataLayer::searchInRowSet('column_name', $audit_column['column_name'], $columns);
+
+        if ($columns[$key]['is_nullable']==='NO')
+        {
+          $columns[$key]['column_type'] = sprintf('%s not null', $columns[$key]['column_type']);
+        }
         if (isset($audit_column['value_type']))
         {
           $columns[$key]['value_type'] = $audit_column['value_type'];
@@ -316,7 +321,7 @@ private function resolveCanonicalAuditColumns()
         }
       }
 
-      $this->auditColumnsMetadata = new TableColumnsMetadata($columns, 'AuditColumnMetadata');
+      $this->auditColumnsMetadata = $columns;
     }
   }
 
diff --git a/src/MySql/AuditDiffTable.php b/src/MySql/AuditDiffTable.php
index 92ed3fa..59022ff 100755
--- a/src/MySql/AuditDiffTable.php
+++ b/src/MySql/AuditDiffTable.php
@@ -117,7 +117,8 @@ public function removeMatchingColumns()
       {
         if (isset($audit) && isset($config))
         {
-          if ($audit->getProperty('column_type')==$config->getProperty('column_type'))
+          $check = $this->compareCollationCharSetName($audit, $config);
+          if ($audit->getProperty('column_type')==$config->getProperty('column_type') && $check)
           {
             if (isset($auditColumn))
             {
@@ -130,21 +131,8 @@ public function removeMatchingColumns()
       {
         if (isset($audit) && isset($config))
         {
-          $config_character_set_name = $config->getProperty('character_set_name');
-          $config_collation_name     = $config->getProperty('collation_name');
-          $audit_character_set_name  = $audit->getProperty('character_set_name');
-          $audit_collation_name      = $audit->getProperty('collation_name');
-
-          $data_character_set_name = $data->getProperty('character_set_name');
-          $data_collation_name     = $data->getProperty('collation_name');
-
-          if (
-            $audit->getProperty('column_type')==$data->getProperty('column_type')
-            && $audit_character_set_name==$data_character_set_name
-            && $audit_character_set_name==$config_character_set_name
-            && $audit_collation_name==$config_collation_name
-            && $audit_collation_name==$data_collation_name
-          )
+          $check = $this->compareCollationCharSetName($data, $audit, $config);
+          if ($audit->getProperty('column_type')==$data->getProperty('column_type') && $check)
           {
             $metadata->removeColumn($columnName);
           }
@@ -183,6 +171,48 @@ private function addNotNull($theColumns)
     return $modifiedColumns;
   }
 
+  //--------------------------------------------------------------------------------------------------------------------
+  /**
+   * Compare collations and character set names.
+   *
+   * @param MultiSourceColumnMetadata      $audit  Column information from audit schema.
+   * @param MultiSourceColumnMetadata      $config Column information from config file.
+   * @param MultiSourceColumnMetadata|null $data   Column information from data schema.
+   *
+   * @return array
+   */
+  private function compareCollationCharSetName($audit, $config, $data = null)
+  {
+    $config_character_set_name = $config->getProperty('character_set_name');
+    $config_collation_name     = $config->getProperty('collation_name');
+    $audit_character_set_name  = $audit->getProperty('character_set_name');
+    $audit_collation_name      = $audit->getProperty('collation_name');
+
+    if (isset($data))
+    {
+      $data_character_set_name = $data->getProperty('character_set_name');
+      $data_collation_name     = $data->getProperty('collation_name');
+
+      if ($audit_character_set_name==$data_character_set_name
+        && $audit_character_set_name==$config_character_set_name
+        && $audit_collation_name==$config_collation_name
+        && $audit_collation_name==$data_collation_name
+      )
+      {
+        return true;
+      }
+    }
+    else
+    {
+      if ($audit_character_set_name==$config_character_set_name && $audit_collation_name==$config_collation_name)
+      {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
   //--------------------------------------------------------------------------------------------------------------------
   /**
    * Get the difference between data and audit tables.