Tsql 需要使用T-SQL添加计算字段

我有一个查询，我想在其中添加一个计算字段。我需要添加2013年的预计销售额。计算方法是当前的月数除以一年的总销售额乘以12。我有一个FiscalMonthNum字段，它还不在查询中。有人能告诉我如何添加我需要的字段吗

SELECT
    a.Vendor,
    vn.ACNAME AS Vendor_Name,
    a.FiscalYear,
    a.QtySold,
    a.ExtCost
FROM
    dbo.S2K_VEND vn
    INNER JOIN
(SELECT
    sd.IFPRVN AS Vendor,
    fc.FiscalYear,
    SUM(sd.SBQSHP) AS QtySold,
    SUM(sd.SBEPRC) AS ExtCost
FROM
    dbo.SalesData sd
    LEFT OUTER JOIN dbo.FiscalCalendar fc ON fc.FiscalDate = sd.SBINDT
WHERE
    sd.SBTYPE = 'O'
AND
    sd.SBINDT > '2011-12-31'
AND
    sd.SBCLS NOT IN ('1500')
GROUP BY
    sd.IFPRVN,
    fc.FiscalYear
)a
ON vn.ACVEND = a.Vendor
GROUP BY
    a.Vendor,
    vn.ACNAME,
    a.FiscalYear,
    a.QtySold,
    a.ExtCost

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下面的方法会奏效吗？将销售额除以最大月数，然后乘以12

SELECT
    a.Vendor,
    vn.ACNAME AS Vendor_Name,
    a.FiscalYear,
    a.QtySold,
    a.ExtCost,
    a.PredictedQtySold,
    a.PredictedExtCost
FROM
    dbo.S2K_VEND vn
    INNER JOIN
(SELECT
    sd.IFPRVN AS Vendor,
    fc.FiscalYear,
    12 * (SUM(sd.SBQSHP)/MAX(FiscalMonthNumber)) AS PredictedQtySold,
    12 * (SUM(sd.SBEPRC)/MAX(FiscalMonthNumber)) AS PredictedExtCost,
    SUM(sd.SBQSHP) AS QtySold,
    SUM(sd.SBEPRC) AS ExtCost
FROM
    dbo.SalesData sd
    LEFT OUTER JOIN dbo.FiscalCalendar fc ON fc.FiscalDate = sd.SBINDT
WHERE
    sd.SBTYPE = 'O'
AND
    sd.SBINDT > '2011-12-31'
AND
    sd.SBCLS NOT IN ('1500')
GROUP BY
    sd.IFPRVN,
    fc.FiscalYear
)a
ON vn.ACVEND = a.Vendor
GROUP BY
    a.Vendor,
    vn.ACNAME,
    a.FiscalYear,
    a.QtySold,
    a.ExtCost
;

---

fiscalmonnum

来自哪个表？它必须是2013年的。你的意思是：当fc.FiscalYear='2013/2014'时，PredictedExtCost=CASE，然后是12*（SUM（sd.SBEPRC）/MAX（FiscalMonthNumber）），否则为空结束