Using the $wpdb in wordpress to run SQL commands

Question

I created a simple update command to update a database entry. I want to be able to run any sql statement and update my wordpress database:

<?php    
global $wpdb;
$sql = "UPDATE tablename SET column1='testdata' WHERE id=1";
$results = get_results($sql); ?>

or

$results = query($sql);

No matter what I do I get the error:

Fatal error: Call to a member function get_results() on null in C:\MAMP\htdocs\new\samplesql.php on line 4

Answer 1

Try this instead:

<?php    
include_once("wp-config.php");
include_once("wp-includes/wp-db.php");

$sql = "UPDATE tablename SET column1='testdata' WHERE id=1";
$results = $wpdb->get_results($sql);

You need to include the files where the database object is defined.

Answer 2

The get_results() and query() functions only work when combined with the $wpdb global.

For example:

global $wpdb;
$wpdb->get_results($sql);