How to fetch 2 times in MYSQL PDO without FETCHALL

问题

I have this sample query:

$STH = $DBH->query("SELECT id FROM table");

I want to get the first row and then loop and display all rows. So I use the following to get the first row:

$STH->setFetchMode(PDO::FETCH_ASSOC);
$first_row = $STH->fetch();
$first_row = $first_row['id'];

I use while loop to display all rows again:

while ($list = $STH->fetch()) {      
$id = $list['id'];
echo $id;
}

Now the while skips the first row and I want it to be displayed. Is there an equivalent to mysql_data_seek to reset the pointer again to the first row? I know fetchall can be used but it's bad on memory and wasteful. I could also run the query and limit to 1 but this is not recommended as I have a query that joins multiple tables and would be very slow. Is there any other solution?

Thanks

回答1:

I take that back looks like you can use the cursor orientation contants to select the result... sample code coming... I havent tried this so you may need to play a bit. This is also based on the assumption that a PDO::FETCH_ORI_FIRST acts like a data_seek and leaves the cursor on the first position as opposed to returning it to whatever it was before.

$stmt = $pdo->prepare('SELECT id FROM table', array(PDO::ATTR_CURSOR => PDO::CURSOR_SCROLL));
$stmt->execute();

$first = $pdo->fetch(PDO::FETCH_ASSOC, PDO::FETCH_ORI_FIRST);
$first_row = $first['id'];

// other stuff

// first iteration we rewind to the first record;
$cursor = PDO::FETCH_ORI_FIRST;

while (false !== ($row = $stmt->fetch(PDO::FETCH_ASSOC, $cursor))) {
   $id = $row['id'];
   // successive iterations we hit the "next" record
   $cursor = PDO::FETCH_ORI_NEXT; 
   echo $id;
}

I dont think you can rewind a statement... Assuming these blocks arent seprated by a bunch of intermediary logic id just do it in the loop.

$STH->setFetchMode(PDO::FETCH_COLUMN); // no need to pull an array
$count = 0;
while ($id = $STH->fetch()) {      
  if($count === 0) {
   $first_row = $id;
  }
  echo $id;
  $count++;
}

回答2:

Could you just use a do...while loop instead?

$STH->setFetchMode(PDO::FETCH_ASSOC);
$list = $STH->fetch();
$first_id = $list['id'];

do {
  $id = $list['id'];
  echo $id;
} while ($list = $STH->fetch());

回答3:

You can fetch all the result, and then just act on it as an array. So, for instance, you could shift the first result off the front, and then loop over any additional rows:

<?php

$sql = "YOUR QUERY";
$stmt = $pdo->prepare($sql);
$stmt->execute();
$rows = $stmt->fetchAll(PDO::FETCH_ASSOC);

// get first row
$firstRow = array_shift($rows);

// loop over remaining rows
foreach ($rows as $row) {
    // do something
}

来源：https://stackoverflow.com/questions/14103202/how-to-fetch-2-times-in-mysql-pdo-without-fetchall

标签

php

mysql

pdo

while-loop

fetch