PHP + MySQL查询->此SQL有什么问题（简短）

Question

I have finally graduated from MS Access to MySQL. Unfortunately, I can't even get a query right. Can someone please tell me what's wrong? I keep getting the 'invalid query' message that I specified in the php.

<?php
@ $db = mysql_connect('localhost', 'root', 'root', 'newdatabase');
if (!$db) {
    die ('Failed to connect to the database.');
}


$query = "SELECT first FROM demographics";
$result = mysql_query($query);

if (!$result) {
    die('invalid query');
}

while ($row = mysql_fetch_assoc($result)) {
    echo $row['first'];
}

?>

Also, the book I am reading tells me to use:

new mysqli('localhost', 'root', 'root', 'newdatabase')

to connect as opposed to the

mysql_connect

I used in the above code. I haven't been able to connect to the db with new mysqli . Does it matter which one I use?

Answer 1

The fourth parameter to mysql_connect() is not the database name. It is a boolean specifying whether or not to establish an additional new connection or use an existing one. Most often, it is omitted. Use mysql_select_db() to choose the database. Since you have not selected a database in your code, your query is likely failing.

$db = mysql_connect('localhost', 'root', 'root');
if (!$db) echo mysql_error();
else mysql_select_db("database");

Note I have removed the @ from the mysql_connect() call. @ suppresses errors, and was probably preventing you from seeing what was going wrong with your connection.

When testing the success or failure of a query, don't die() . Instead echo out mysql_error() while developing your application. In production, you can replace the echo by writing to error_log() instead.

if (!$result) {
  echo mysql_error();
}

As for using MySQLi instead of the basic mysql_* functions, MySQLi can be used in an object oriented fashion and also offers prepared statements, which can be both more efficient to use and more secure. As mentioned in comments above, PDO is often recommended as the most flexible API for interacting with an RDBMS from PHP.