Question

我是Mysqli_ *的新手，我收到了这些错误：

警告：mysqli_select_db（）期望参数1为mysqli，string   在第11行的D：\ Hosting \ 9864230 \ html \ includes \ connection.php中给出

警告：mysqli_error（）正好需要1个参数，给出0   第13行的D：\ Hosting \ 9864230 \ html \ includes \ connection.php

数据库选择失败：

<?php
require("constants.php");

// 1. Create a database connection
$connection = mysqli_connect(DB_SERVER,DB_USER,DB_PASS);
if (!$connection) {
    die("Database connection failed: " . mysqli_error());
}

// 2. Select a database to use 
$db_select = mysqli_select_db(DB_NAME,$connection);
if (!$db_select) {
    die("Database selection failed: " . mysqli_error());
}
?>

Answer 1

你的论点顺序错误。首先根据docs

连接

<?php
require("constants.php");

// 1. Create a database connection
$connection = mysqli_connect(DB_SERVER,DB_USER,DB_PASS);
if (!$connection) {
    die("Database connection failed");
}

// 2. Select a database to use 
$db_select = mysqli_select_db($connection, DB_NAME);
if (!$db_select) {
    die("Database selection failed: " . mysqli_error($connection));
}
?>

Answer 2

// 2. Select a database to use 
$db_select = mysqli_select_db($connection, DB_NAME);
if (!$db_select) {
    die("Database selection failed: " . mysqli_error($connection));
}

你向mysqli_select_db()的参数顺序倒退了。 mysqli_error()要求您提供连接参数。 mysqli_XXX与mysql_XXX不同，这些参数不再是可选的。

另请注意，使用mysqli，您可以在mysqli_connect()中指定数据库：

$connection = mysqli_connect(DB_SERVER, DB_USER, DB_PASS, DB_NAME);
if (!$connection) {
  die("Database connection failed: " . mysqli_connect_error();
}

必须使用mysqli_connect_error()而不是mysqli_error()才能从mysqli_connect()获取错误，因为后者要求您提供有效的连接。

mysqli_select_db（）期望参数1为mysqli，给定字符串

2 个答案: