使用 PHP PDO 扫描 MySql 表中的重复项的正确方法是什么？

Question

Ηow am I supposed to write the PHP script correctly so that it executes as few queries in the database as possible to check for duplicates? I want to know which column is duplicated and get it. I tried to use the PDO exception but I only achieved to get the error code for duplicates, the error message and the trace. I want a way that is more economical and efficient using PDO. (forgive my bad english)

Here is my functionality

    <?php

require 'Connection.php';

class Test extends Connection {

    public function checkForDuplicatedUsernames($username) : String {
        try {
            $statement = $this->connect()->prepare("SELECT username FROM users WHERE username = ?");
        } catch (PDOException $exception){
            return "error code 1"; //Connection error
        }
        $statement->execute([$username]);
        $username = $statement->fetch();
        if ($username !== false) {
            return $username['username'];
        }
        return "go on";
    }

    public function checkForDuplicatedEmails($email) : String {
        try {
            $statement = $this->connect()->prepare("SELECT username FROM users WHERE email = ?");
        } catch (PDOException $exception){
            return "error code 1"; //Connection error
        }
        $statement->execute([$email]);
        $username = $statement->fetch();
        if ($username !== false) {
            return $username['email'];
        }
        return "go on";
    }

    public function setUsersFromStatement() : int {
        if ($this->checkForDuplicatedUsernames('test') === "go on"){
            if ($this->checkForDuplicatedEmails('test') === "go on"){
                try {
                    $sqlSelectString = "INSERT INTO users(username,password,email,firstname,lastname,birthday) VALUES (?,?,?,?,?,?)";
                    //PRIMARY KEY username, UNIQUE email
                    $statement = $this->connect()->prepare($sqlSelectString);
                } catch (PDOException $exception){
                    return -1;
                }
                $statement->execute(['test','test','test','test','test','1984-04-03']);
                $result = $statement->rowCount();
                $statement = null;
                return $result;
            }
            return 3;
        }
        return 4;
    }

}

CONNECTION CLASS

    <?php

class Connection {

    private string $host = "localhost";
    private string $username = "test";
    private string $password = "test";
    private string $dbname = "testdb";

    public function connect(): PDO
    {
        $dataSourceName = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;
        $options = [
            PDO::ATTR_EMULATE_PREPARES   => false,
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
        ];
        return new PDO($dataSourceName, $this->username, $this->password, $options);
    }

}

Answer 1

You can use a single query to check for duplicate email or username.

<?php

require 'Connection.php';

class Test extends Connection {

    public function checkForDuplicatedUsernameOrEmail($username, $email) : string {
        try {
            $statement = $this->connect()->prepare("
                SELECT MAX(username = ?) AS usernameDuplicated, MAX(email = ?) AS emailDuplicated 
                FROM users 
                WHERE username = ? OR email = ?");
            $statement->execute([$username, $email, $username, $email]);
            $row = $statement->fetch(PDO::FETCH_ASSOC);
            if (!$row) {
                return '';
            } elseif ($row['usernameDuplicated']) {
                return 'username';
            } else {
                return 'email';
            }
        } catch (PDOException $exception){
            return false;
        }
    }

    public function setUsersFromStatement() : int {
        $dup = $this->checkForDuplicatedUsernameOrEmail('test', 'test');
        if ($dup == 'username') {
            return 4;
        } elseif ($dup == 'email') {
            return 3;
        }
        try {
            $sqlSelectString = "INSERT INTO users(username,password,email,firstname,lastname,birthday) VALUES (?,?,?,?,?,?)";
            //PRIMARY KEY username, UNIQUE email
            $statement = $this->connect()->prepare($sqlSelectString);
        } catch (PDOException $exception){
            return -1;
        }
        $statement->execute(['test','test','test','test','test','1984-04-03']);
        $result = $statement->rowCount();
        $statement = null;
        return $result;
    }

}