How to define table prefix in variable

Question

I want to define prefix in variable

global $wpdb;
    $prefix = 'qa_';
    $titles = $wpdb->get_results("
        SELECT title
        FROM "$prefixpages"
        }
    ");

Can anyone guide why its not working and hot to make it works.

Answer 1

if you need to query from table qa_tages:

global $wpdb;
$prefix = 'qa_';
$titles = $wpdb->get_results("
    SELECT title
    FROM ${prefix}pages
    }
");

OR same line:

    ..."
    FROM ".$prefix."pages
    "...

if you need contents of $qa_pages variable:

global $wpdb;
$prefix = 'qa_';
$titles = $wpdb->get_results("
    SELECT title
    FROM ".${$prefix.'pages'}."
    }
");