How can the missing quotation marks at the end of the SQL query assignment in the PHP code be corrected to avoid errors?

The missing quotation marks at the end of the SQL query assignment in the PHP code can be corrected by simply adding the missing quotation marks to close the string properly. This will ensure that the SQL query is formed correctly and avoid any syntax errors when executing the query.

$query = "SELECT * FROM users WHERE username = 'example_user'";