粗略的方法是设置balance 到\'mt1.meta_value\' 然后使用\'posts_request\' 筛选以删除转义引号：

$args = array(
  \'post_type\' => \'post\', // maybe not
  \'meta_query\' => array(
    array(
      \'key\' => \'balance\',
      \'compare\' => \'>=\',
      \'value\' => \'mt1.meta_value\', // this will be treated as a string
      \'type\' => \'NUMERIC\'
    ),
    // this is to force adding the needed JOIN clause
    array(
      \'key\' => \'monthly_price\', 
      \'compare\' => \'EXISTS\' 
    ),
    \'relation\' => \'AND\'
  )
);

$closure = function( $sql ) {
  // remove single quotes around \'mt1.meta_value\'
  return str_replace( "\'mt1.meta_value\'", "mt1.meta_value", $sql );
};

add_filter( \'posts_request\', $closure );

$query = new \\WP_Query( $args ); // this is your query :)

remove_filter( \'posts_request\', spl_object_hash( $closure ) );