我可以使用SQL同时计算行数和获取列值吗？

Question

I'm using a SELECT COUNT(*) in order to verify that a user exists with PHP PDO and MySQL. I'd also like to get a specific column value. There is only ever one value/row or no value/row per user.

I'm trying to do something like this:

$stmt = $link->prepare('SELECT COUNT(*) AND column FROM table WHERE user=:user');

What I'm hoping to get back is, 1, and the column value. Where I can then bind the column value to a variable.

If not, I'll have to first do the SELECT COUNT(*) then do another query to get the column name after verifying that the user and this column exists from the SELECT COUNT(*) query.

Answer 1

You just need to think a little.

"count(*)" is not a special method "to verify that a user exists". It's just a query where you select count because you just have no idea what to select else.

But as long as you have a column to select, you don't need no counts anymore.

Therefore, just select your value, and as long as you are getting it, you can tell that a user exists

$stmt = $link->prepare('SELECT column FROM table WHERE user=:user');
$stmt->execute([$user]);
$col = $stmt->fetchColumn();

if ($col) {
    // user exists
    $something = $col; // use $col as you wanted
}

While selecting count() and a column without a group by operator is a tricky query, and you should avoid it in general.

Answer 2

SELECT count(*), column FROM table where user=:user

It's what you want no ?

Otherwise you can count the number of result in php

$pdo = new PDO('mysql:host=XXX.fr.mysql;dbname=YYYY', 'ZZZ', 'TTT', $pdo_options);

    $response = $pdo->query('SELECT column FROM table');
    $count = 0;
    while ($data = $response->fetch())
    {
        $count++;
    }
    $reponse->closeCursor();