Просто создайте анонимную функцию:
var foo = new function () {
this.a = 5;
this.b = 6;
this.c = this.a + this.b;
};
У вас странное определение «разницы». Для этого используйте подзапрос:
SELECT CONCAT('£ ', n1) AS Total_N1,
CONCAT('£ ', n2) AS Total_N2,
100 * (N1 - N2) / (N1+N2) / 2 as diff
FROM (SELECT SUM(CASE WHEN t1.col_type = 'N1' THEN t2.qty * t1.price ELSE 0 END) as n1,
SUM(CASE WHEN t1.col_type = 'N2' THEN t2.qty * t1.price ELSE 0 END) as n2
FROM t2 INNER JOIN
t1
ON t2.col_id = t1.col_id
) t