Add to JSON object

Add to JSON object

Not sure where this question belongs so I'll try here.

I am trying to add { "tag" : "bridge"} to the end of a JSON array of objects.

I have manipulated the return query in php like this:

  1. $DB="bridge";      

    }

    echo json_encode(plainQuery($DB, $query));

    }       


    function plainQuery($db, $query) {
       
      //echo "query 53 ".$query."\n";
     
           $cxn = mysqli_connect(HOST,USER,PW,$db) or die("line 22 bridgeQueries.php - Couldn't connect to server");

         if (mysqli_connect_errno($cxn)) {
                printf("Connect failed: %s\n", mysqli_error($cxn));
                exit();
        };

                $result = mysqli_query($cxn, $query) or exit( mysqli_error( $cxn ));  // delete current data
               while($row = mysqli_fetch_assoc($result)) {  
               $rows[]=$row;

             }

        $rows[]="{".'"tag"'.' : '. '"'.$db.'"'."}";
         
    return $rows;

The last part of the returned JSON obj is like so:

,{"id":"176","playdate":"2015-02-09","player":"Rodriguez, Terri","score":"1190"},
{"id":"177","playdate":"2015-03-02","player":"Rupp, Kathy","score":"2750"},

"{\"tag\" : \"bridge\"}"]

My question is how can I get this in proper format like {"tag" : "bridge"}? 

Should I try to add this last object after it is returned by AJAX in the success callback function?