Question

我一直在检查检查重复用户名的最佳方法我看到有人说EXISTS性能更好，这个公式好吗？还是有更好的？ IF EXISTS和SELECT EXISTS以及WHEN EXISTS之间有什么区别？是否可以在代码中合并电子邮件并同时检查电子邮件和用户名？或者将两个quires分开是否更好？

$username = $_POST['username'];
    $stmt = $conn->prepare("SELECT EXISTS (SELECT username FROM users WHERE username = :username)");
    $stmt->execute([':username' => $username]);
    if ($stmt->fetchColumn() > 0) {
        echo "Username is already taken.";
    }

Answer 1

如果为true则返回bit，然后返回1，否则返回False 0

    SELECT CASE WHEN EXISTS (
        SELECT username FROM users WHERE username = :username
    )
    THEN CAST(1 AS BIT)
    ELSE CAST(0 AS BIT)
    END AS result

Answer 2

您可以将用户名或电子邮件设置为唯一键。然后使用try .. catch

try {
  // do your insert query. If it fails to insert, it will throw error message
  // Also need to turn on error exception mode for PDO attribute
} catch (PDOException $e) {
  echo $e->getMessage();
}

您可以使用SQL：

SQL COUNT

$ stmt = $ conn-＆gt; prepare（＆＃39; SELECT COUNT（用户名）AS total FROM users WHERE username =：username＆＃39;）;

//或$ stmt = $ conn-＆gt;准备（＆＃39; SELECT COUNT（用户名）AS用户总数= username =：username AND email =：email＆＃39;）;

$ stmt-＆gt; bindParam（＆＃39;：username＆＃39;，$ username）; $ stmt-＆gt; bindParam（＆＃39;：email＆＃39;，$ email）; $ stmt-＆GT;执行（）; $ row = $ stmt-＆gt; fetch（PDO :: FETCH_OBJ）; if（$ row-＆gt; total＆gt; 0）{ echo＆＃39;用户名/电子邮件已经拍摄。＆＃39 ;; }

[1]：http://php.net/manual/en/pdo.setattribute.php

使用EXISTS检查重复的用户名

2 个答案: