sql - postgresql and INSERT variables -

i'm close stuck. pull user name drupal , store in variable called $username, want store in column called username. below code throws error

        $sql = "insert sheet_tbl (site_id, user_id, eventdate, eventtime, username) values ('$_post[site_id]','$_post[user_id]','$_post[eventdate]','$_post[eventtime]',$username)"; 

error

warning: pg_query() [function.pg-query]: query failed: error: syntax error @ or near ")" @ character 112 in /var/www/html/drupal1/includes/common.inc(1743) : eval()'d code on line 30. 

i pull user name using:

 user name: <?php   global $user;  echo $user->name;  $username = $user->name;  ?> 

if echo variable result = admin

you did not put username in quotes. replace

,$username)"; 

with

,'$username')"; 

and btw should not put unescaped user input in sql statements. can lead sql injections. see here