[Deff]

var db = [
 ['a', 'b', '1', '2'],
 ['a', 'c', '3', '4'],
 ['b', 'd', '5', '6']
];


var dbIndex0;
var concat='';

var i, j;
for(i=0; i<db.length; i++) {
  if(db[i][0]=='a'&&db[i][1]=='b'){
     dbIndex0 = i;
     for(j=2; j<db[i].length; j++) {
        concat+=db[i][j];
     }
     break;
  }
}
alert(dbIndex0+'\n'+concat)