php PDO fetchAll() - 虽然不工作，但 foreach 工作

2021-12-26 00:00:00 while-loop foreach php pdo fetchall

我想知道我是做得好还是 fetchAll() 不适用于 WHILE.

I would like to know if i'm doing fine OR fetchAll() doesn't work with WHILE.

举个例子

$db=new PDO("mysql:host=" .$dbhost. "; dbname=" . $dbname, $dbuser, $dbpass);

$page=$db->prepare("SELECT * FROM page");
$page->execute();

foreach ($page->fetchAll(PDO::FETCH_ASSOC) as $row) {

//echo a row
//is working
}

但是，我如果尝试使用 while 循环

however, i if try looping with a while

while ($row=$page->fetchAll(PDO::FETCH_ASSOC)){

//echo a row
//Show empty
}

我尝试只使用 fetch()，它起作用了，我的问题是:为什么 fetchAll() 不能与WHILE"一起使用?

i tryed to use only fetch(), it was working, my question: why fetchAll() doesn't work with "WHILE" ?

推荐答案

Fetch all 返回结果集中剩余的所有记录.考虑到这一点，您的 foreach 能够按预期迭代结果集.

Fetch all returns all of the records remaining in the result set. With this in mind your foreach is able to iterate over the result set as expected.

对于等效的 while 实现应该使用 $page->fetch(PDO::FETCH_ASSOC);

For the equivalent while implementation should use $page->fetch(PDO::FETCH_ASSOC);

while ($row = $page->fetch(PDO::FETCH_ASSOC)){
   // do something awesome with row
}

如果你想使用一段时间并获取所有你能做的

if you want to use a while and fetch all you can do 

$rows = $page->fetchAll(PDO::FETCH_ASSOC);

// use array_shift to free up the memory associated with the record as we deal with it
while($row = array_shift($rows)){
   // do something awesome with row
}

尽管有一句警告:fetch all 将完全做到这一点，如果结果大小很大，则会对您机器上的资源造成压力.只有在我知道结果集很小的情况下，我才会这样做，或者我通过对查询应用限制来强制这样做.

A word of warning though: fetch all will do exactly that, if the result size is large it will stress the resources on your machine. I would only do this if I know that the result set will be small, or I'm forcing that by applying a limit to the query.

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