code: public function addColumn($table, $column, $type)
      {
          $sql = $this->db->getQueryBuilder()->addColumn($table, $column, $type);
  
          return $this->setSql($sql)->requireTableSchemaRefresh($table);
      }
docs: Creates a SQL command for adding a new DB column.
  @param string $table the table that the new column will be added to. The table name will be properly quoted by the method.
  @param string $column the name of the new column. The name will be properly quoted by the method.
  @param string $type the column type. [[\yii\db\QueryBuilder::getColumnType()]] will be called
  to convert the give column type to the physical one. For example, `string` will be converted
  as `varchar(255)`, and `string not null` becomes `varchar(255) not null`.
  @return $this the command object itself