diff --git a/framework/db/ColumnSchemaBuilder.php b/framework/db/ColumnSchemaBuilder.php
index 5262b66993..6db12c889b 100644
--- a/framework/db/ColumnSchemaBuilder.php
+++ b/framework/db/ColumnSchemaBuilder.php
@@ -372,7 +372,7 @@ class ColumnSchemaBuilder extends Object
      */
     protected function buildCommentString()
     {
-        return $this->comment !== null ? " COMMENT " . $this->db->quoteValue($this->comment) : '';
+        return '';
     }
 
     /**
diff --git a/framework/db/cubrid/ColumnSchemaBuilder.php b/framework/db/cubrid/ColumnSchemaBuilder.php
index 0782a03882..c39e4b7387 100644
--- a/framework/db/cubrid/ColumnSchemaBuilder.php
+++ b/framework/db/cubrid/ColumnSchemaBuilder.php
@@ -43,6 +43,14 @@ class ColumnSchemaBuilder extends AbstractColumnSchemaBuilder
         return $this->isFirst ? ' FIRST' : '';
     }
 
+    /**
+     * @inheritdoc
+     */
+    protected function buildCommentString()
+    {
+        return $this->comment !== null ? " COMMENT " . $this->db->quoteValue($this->comment) : '';
+    }
+
     /**
      * @inheritdoc
      */
diff --git a/framework/db/mssql/ColumnSchemaBuilder.php b/framework/db/mssql/ColumnSchemaBuilder.php
deleted file mode 100644
index d08b2a4135..0000000000
--- a/framework/db/mssql/ColumnSchemaBuilder.php
+++ /dev/null
@@ -1,27 +0,0 @@
-<?php
-/**
- * @link http://www.yiiframework.com/
- * @copyright Copyright (c) 2008 Yii Software LLC
- * @license http://www.yiiframework.com/license/
- */
-
-namespace yii\db\mssql;
-
-use yii\db\ColumnSchemaBuilder as AbstractColumnSchemaBuilder;
-
-/**
- * ColumnSchemaBuilder is the schema builder for Oracle databases.
- *
- * @author Vasenin Matvey <vaseninm@gmail.com>
- * @since 2.0.6
- */
-class ColumnSchemaBuilder extends AbstractColumnSchemaBuilder
-{
-    /**
-     * @inheritdoc
-     */
-    protected function buildCommentString()
-    {
-        return '';
-    }
-}
diff --git a/framework/db/mssql/Schema.php b/framework/db/mssql/Schema.php
index ba052ccf62..2f372a3ef8 100644
--- a/framework/db/mssql/Schema.php
+++ b/framework/db/mssql/Schema.php
@@ -124,15 +124,6 @@ class Schema extends \yii\db\Schema
         return new QueryBuilder($this->db);
     }
 
-    /**
-     * @inheritdoc
-     * @return ColumnSchemaBuilder column schema builder instance
-     */
-    public function createColumnSchemaBuilder($type, $length = null)
-    {
-        return new ColumnSchemaBuilder($type, $length);
-    }
-
     /**
      * Loads the metadata for the specified table.
      * @param string $name table name
diff --git a/framework/db/mysql/ColumnSchemaBuilder.php b/framework/db/mysql/ColumnSchemaBuilder.php
index 24e3eb0018..8c338ec400 100644
--- a/framework/db/mysql/ColumnSchemaBuilder.php
+++ b/framework/db/mysql/ColumnSchemaBuilder.php
@@ -43,6 +43,14 @@ class ColumnSchemaBuilder extends AbstractColumnSchemaBuilder
         return $this->isFirst ? ' FIRST' : '';
     }
 
+    /**
+     * @inheritdoc
+     */
+    protected function buildCommentString()
+    {
+        return $this->comment !== null ? " COMMENT " . $this->db->quoteValue($this->comment) : '';
+    }
+
     /**
      * @inheritdoc
      */
diff --git a/framework/db/oci/ColumnSchemaBuilder.php b/framework/db/oci/ColumnSchemaBuilder.php
index 1dda4cb041..edc8a773c6 100644
--- a/framework/db/oci/ColumnSchemaBuilder.php
+++ b/framework/db/oci/ColumnSchemaBuilder.php
@@ -13,7 +13,8 @@ use yii\db\ColumnSchemaBuilder as AbstractColumnSchemaBuilder;
  * ColumnSchemaBuilder is the schema builder for Oracle databases.
  *
  * @author Vasenin Matvey <vaseninm@gmail.com>
- * @since 2.0.6
+ * @author Chris Harris <chris@buckshotsoftware.com>
+ * @since 2.0.8
  */
 class ColumnSchemaBuilder extends AbstractColumnSchemaBuilder
 {
@@ -60,12 +61,4 @@ class ColumnSchemaBuilder extends AbstractColumnSchemaBuilder
         }
         return $this->buildCompleteString($format);
     }
-
-    /**
-     * @inheritdoc
-     */
-    protected function buildCommentString()
-    {
-        return '';
-    }
 }
diff --git a/framework/db/pgsql/ColumnSchemaBuilder.php b/framework/db/pgsql/ColumnSchemaBuilder.php
deleted file mode 100644
index 0e2fb59b48..0000000000
--- a/framework/db/pgsql/ColumnSchemaBuilder.php
+++ /dev/null
@@ -1,27 +0,0 @@
-<?php
-/**
- * @link http://www.yiiframework.com/
- * @copyright Copyright (c) 2008 Yii Software LLC
- * @license http://www.yiiframework.com/license/
- */
-
-namespace yii\db\pgsql;
-
-use yii\db\ColumnSchemaBuilder as AbstractColumnSchemaBuilder;
-
-/**
- * ColumnSchemaBuilder is the schema builder for Postgres databases.
- *
- * @author Vasenin Matvey <vaseninm@gmail.com>
- * @since 2.0.6
- */
-class ColumnSchemaBuilder extends AbstractColumnSchemaBuilder
-{
-    /**
-     * @inheritdoc
-     */
-    protected function buildCommentString()
-    {
-        return '';
-    }
-}
diff --git a/framework/db/pgsql/Schema.php b/framework/db/pgsql/Schema.php
index 86402e4cfb..b83fdcdf17 100644
--- a/framework/db/pgsql/Schema.php
+++ b/framework/db/pgsql/Schema.php
@@ -118,15 +118,6 @@ class Schema extends \yii\db\Schema
         return new QueryBuilder($this->db);
     }
 
-    /**
-     * @inheritdoc
-     * @return ColumnSchemaBuilder column schema builder instance
-     */
-    public function createColumnSchemaBuilder($type, $length = null)
-    {
-        return new ColumnSchemaBuilder($type, $length);
-    }
-
     /**
      * Resolves the table name and schema name (if any).
      * @param TableSchema $table the table metadata object
diff --git a/framework/db/sqlite/ColumnSchemaBuilder.php b/framework/db/sqlite/ColumnSchemaBuilder.php
index 0678029c58..956170af06 100644
--- a/framework/db/sqlite/ColumnSchemaBuilder.php
+++ b/framework/db/sqlite/ColumnSchemaBuilder.php
@@ -44,12 +44,4 @@ class ColumnSchemaBuilder extends AbstractColumnSchemaBuilder
 
         return $this->buildCompleteString($format);
     }
-
-    /**
-     * @inheritdoc
-     */
-    protected function buildCommentString()
-    {
-        return '';
-    }
 }