mysqli_select_db() expects parameter 1 to be mysqli, string given

Question

I am new to Mysqli_* and I am getting these errors:

Warning: mysqli_select_db() expects parameter 1 to be mysqli, string given in D:\Hosting\9864230\html\includes\connection.php on line 11

Warning: mysqli_error() expects exactly 1 parameter, 0 given in D:\Hosting\9864230\html\includes\connection.php on line 13

Database selection failed:

<?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());
}
?>

You have the wrong parameter order, set `$connection` before `DB_NAME` at your call to `mysqli_select_db()`. I don't think this question shows any search effort at all, try google or look at php.net next time. — Cyclonecode, Dec 20 '12 at 19:35
Please learn about functions first before you use them, that includes learning about the meaning of each parameter as well as learning about the return value and the type of error handling that is used with the function. — hakre, Dec 20 '12 at 19:41
Please read https://stackoverflow.com/questions/58808332/should-we-ever-check-for-mysqli-connect-errors-manually — Dharman, Dec 18 '19 at 07:17

Chris McKnight · Accepted Answer · 2019-12-31T00:01:45.057

60

Your arguments are in the wrong order. The connection comes first according to the docs

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

// 1. Create a database connection
$connection = mysqli_connect(DB_SERVER,DB_USER,DB_PASS);

if (!$connection) {
    error_log("Failed to connect to MySQL: " . mysqli_error($connection));
    die('Internal server error');
}

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

?>

edited Dec 31 '19 at 00:01

answered Dec 20 '12 at 19:35

Chris McKnight

8,540
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31

Please read https://stackoverflow.com/questions/58808332/should-we-ever-check-for-mysqli-connect-errors-manually – Dharman Dec 18 '19 at 07:15

Barmar · Answer 2 · 2012-12-20T19:41:37.800

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

You got the order of the arguments to mysqli_select_db() backwards. And mysqli_error() requires you to provide a connection argument. mysqli_XXX is not like mysql_XXX, these arguments are no longer optional.

Note also that with mysqli you can specify the DB in mysqli_connect():

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

You must use mysqli_connect_error(), not mysqli_error(), to get the error from mysqli_connect(), since the latter requires you to supply a valid connection.

mysqli_select_db() expects parameter 1 to be mysqli, string given

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