name         month    avgBefore   avgAfter
P.Anderson     3          13         35

SELECT
    c.name, c.code,
    MONTH(t.DateTime) AS minas,
    AVG(t.charged_amount) AS total
FROM
    dbo.customers AS c
INNER JOIN
    dbo.accounts AS a ON c.code = a.customer_code
INNER JOIN
    dbo.creditcard AS cc ON a.acc_number = cc.acc_number
INNER JOIN
    dbo.transactions AS t ON cc.cc_number = t.cc_number
INNER JOIN
    dbo.shop AS s ON t.shop_code = s.shop_code
WHERE
    (YEAR(t.DateTime) = 2009)
GROUP BY
    c.name, c.code, MONTH(t.DateTime)

create view [Dec](name, code, minas, averg)
as
    select * from v1
    where minas = 12

select
    v1.name, v1.code, v1.minas, sum(total)
from
    v1, Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, [Dec]
where
    v1.minas <= Jan.minas or v1.minas <= Feb.minas or
    v1.minas <= Mar.minas or v1.minas <= Apr.minas or
    v1.minas <= May.minas or v1.minas <= Jun.minas or
    v1.minas <= Jul.minas or v1.minas <= Aug.minas or
    v1.minas <= Sep.minas or v1.minas <= Oct.minas or
    v1.minas <= Nov.minas or v1.minas <= [Dec].minas
group by
    v1.name,v1.code,v1.minas

select
    v1.name, v1.code, v1.minas, sum(v1.total)
from
    v1, Jan as v2, Feb as v3
where
    v1.code = v2.code and v1.code = v3.code
group by
    v1.name, v1.code, v1.minas

Nelson J. Arredondo 100606 1 75
Nelson J. Arredondo 100606 2 100
Nelson J. Arredondo 100606 5 250