在最新的PHP版本中，它由PDO::MYSQL_ATTR_FOUND_ROWS属性控制. 当设置为true时，根据 doc ，效果是:

On recent PHP versions, it's controlled by the PDO::MYSQL_ATTR_FOUND_ROWS attribute. When set to true, according to the doc, the effect is:

Return the number of found (matched) rows, not the number of changed rows.