如果数据库不存在，请使用mysqli+php创建数据库 - Create DB if not exists using mysqli + php

Create DB if not exists using mysqli + php

如果数据库名称不存在，我将尝试使用mysqli创建数据库，使用以下代码：

<?php
$link = mysqli_connect("localhost", "root", "", "php1") ; 
if(mysqli_connect_errno()){
    echo mysqli_connect_error();
    $query = "CREATE DATABASE php1";
    if(mysqli_query($link, $query)){
        echo "Success";
    } else {
        echo "Failure";
    }
}

?>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>        
        <a href="signup.php"><button type="button">Sign Up!</button></a>
        <a href="login.php"><button type="button">Log In</button></a>
    </body>
</html>

代码检查数据库&它不存在。接下来，如果数据库不存在，我想创建它，但我总是收到以下错误：

Warning: mysqli_connect(): (HY000/1049): Unknown database 'php1' in E:'xampp'htdocs'PhpProject1'index.php on line 3
Unknown database 'php1'
Warning: mysqli_query() expects parameter 1 to be mysqli, boolean given in E:'xampp'htdocs'PhpProject1'index.php on line 7
Failure

这样我就无法创建新的数据库。有人知道如何纠正这一点吗？

修复此问题的三个步骤：

连接时不要指定数据库名称
您的SQL语句应该是CREATE DATABASE IF NOT EXISTS php1
调用mysqli_select_db($link, 'php1')使其成为连接的默认数据库

// Enable error reporting for mysqli
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
// Connection to MySQL server without database name.
$connect = new mysqli('localhost', 'my_user', 'my_password');
// Set the desired charset after establishing a connection
$connect->set_charset('utf8mb4');
// Create database if not exists.
$databaseName = 'database_name';
$query = 'CREATE DATABASE IF NOT EXISTS ' . $databaseName;
// Use the new database for all future SQL queries.
mysqli_select_db($connect, $databaseName);

有关mysqli_connect的详细信息：https://www.php.net/manual/en/mysqli.construct.php

$connection = '';
$connection = new mysqli("db", "root", "example");
$query = mysqli_query($connection, "SHOW DATABASES LIKE 'company'");
$result = mysqli_num_rows($query);
if($result <=0){
$create = mysqli_query($connection, "CREATE DATABASE IF NOT EXISTS company;");
echo "Database created successifully";
}