code: public function selectFunc( $func, $field, $alias = null ) { // @codingStandardsIgnoreLine
  		$field = "$func({$field})";
  		if ( ! is_null( $alias ) ) {
  			$field .= " as {$alias}";
  		}
  		$this->statements['select'][] = $field;
  
  		return $this;
  	}
docs: Shortcut to add a function
  
  @param string $func  Function name.
  @param string $field Column name.
  @param string $alias (Optional) Column alias.
  
  @return self The current query builder.