diff --git a/framework/db/Command.php b/framework/db/Command.php
index f0089a31df..0856c88ce1 100644
--- a/framework/db/Command.php
+++ b/framework/db/Command.php
@@ -631,13 +631,24 @@ class Command extends Component
      *
      * The columns in the new table should be specified as name-definition pairs (e.g. 'name' => 'string'),
      * where name stands for a column name which will be properly quoted by the method, and definition
-     * stands for the column type which can contain an abstract DB type.
+     * stands for the column type which must contain an abstract DB type. 
+     * 
      * The method [[QueryBuilder::getColumnType()]] will be called
      * to convert the abstract column types to physical ones. For example, `string` will be converted
      * as `varchar(255)`, and `string not null` becomes `varchar(255) not null`.
      *
      * If a column is specified with definition only (e.g. 'PRIMARY KEY (name, type)'), it will be directly
      * inserted into the generated SQL.
+     * 
+     * Example usage:
+     * ```php
+     * Yii::$app->db->createCommand()->createTable('post', [
+     *     'id' => 'pk',
+     *     'title' => 'string',
+     *     'text' => 'text',
+     *     'column_name double precision null default null',
+     * ]);                   
+     * ```
      *
      * @param string $table the name of the table to be created. The name will be properly quoted by the method.
      * @param array $columns the columns (name => definition) in the new table.
diff --git a/framework/db/Migration.php b/framework/db/Migration.php
index be61749514..975898cd53 100644
--- a/framework/db/Migration.php
+++ b/framework/db/Migration.php
@@ -305,12 +305,24 @@ class Migration extends Component implements MigrationInterface
      *
      * The columns in the new  table should be specified as name-definition pairs (e.g. 'name' => 'string'),
      * where name stands for a column name which will be properly quoted by the method, and definition
-     * stands for the column type which can contain an abstract DB type.
+     * stands for the column type which must contain an abstract DB type.
      *
      * The [[QueryBuilder::getColumnType()]] method will be invoked to convert any abstract type into a physical one.
      *
      * If a column is specified with definition only (e.g. 'PRIMARY KEY (name, type)'), it will be directly
      * put into the generated SQL.
+     * 
+     * Example usage:
+     * ```php
+     * class m200000_000000_create_table_fruits extends \yii\db\Migration
+     * {
+     *     public function safeUp()
+     *     {
+     *          $this->createTable('{{%fruits}}', [
+     *              // ...              
+     *              'column_name double precision null default null',
+     * ```
+
      *
      * @param string $table the name of the table to be created. The name will be properly quoted by the method.
      * @param array $columns the columns (name => definition) in the new table.
diff --git a/framework/db/QueryBuilder.php b/framework/db/QueryBuilder.php
index b96ffe28ef..114116e67c 100644
--- a/framework/db/QueryBuilder.php
+++ b/framework/db/QueryBuilder.php
@@ -692,7 +692,7 @@ class QueryBuilder extends \yii\base\BaseObject
      *
      * The columns in the new table should be specified as name-definition pairs (e.g. 'name' => 'string'),
      * where name stands for a column name which will be properly quoted by the method, and definition
-     * stands for the column type which can contain an abstract DB type.
+     * stands for the column type which must contain an abstract DB type.
      * The [[getColumnType()]] method will be invoked to convert any abstract type into a physical one.
      *
      * If a column is specified with definition only (e.g. 'PRIMARY KEY (name, type)'), it will be directly
@@ -705,6 +705,7 @@ class QueryBuilder extends \yii\base\BaseObject
      *  'id' => 'pk',
      *  'name' => 'string',
      *  'age' => 'integer',
+     *  'column_name double precision null default null', # definition only example
      * ]);
      * ```
      *