答案在文档中
bindParam：
与PDOStatement :: bindValue（）不同，该变量被绑定为引用，并且仅在调用PDOStatement ::
execute（）时进行评估。
和
execute
调用PDOStatement :: bindParam（）将PHP变量绑定到参数标记：绑定变量将其值作为输入传递，并接收其关联参数标记的输出值（如果有）
例：
$value = 'foo';$s = $dbh->prepare('SELECt name FROM bar WHERe baz = :baz');$s->bindParam(':baz', $value); // use bindParam to bind the variable$value = 'foobarbaz';$s->execute(); // executed with WHERe baz = 'foobarbaz'要么
$value = 'foo';$s = $dbh->prepare('SELECt name FROM bar WHERe baz = :baz');$s->bindValue(':baz', $value); // use bindValue to bind the variable's value$value = 'foobarbaz';$s->execute(); // executed with WHERe baz = 'foo'
