从上一行中选择计算出的值

Question

我需要计算仓库的每日库存。

我有2张桌子

create table #Stock_Beginning 
(
    WH_CODE VARCHAR(4),
    MNTH VARCHAR(6),
    MODELCODE VARCHAR(5),
    STOCKMONTH INT
)

INSERT INTO #Stock_Beginning 
VALUES ('WH01', '201806', 'KD001', 10000)

create table #WH_TRANS 
(
    WH_CODE VARCHAR(4),
    [DAY] DATETIME,
    MODELCODE VARCHAR(5),
    USEDQTY INT,
    ORDERQTY INT
)

INSERT INTO #WH_TRANS 
VALUES ('WH01', '2018-06-01', 'KD001', 1000, 0),
       ('WH01', '2018-06-02', 'KD001', 800, 1000),
       ('WH01', '2018-06-03', 'KD001', 700, 0),
       ('WH01', '2018-06-04', 'KD001', 1000, 2000),
       ('WH01', '2018-06-05', 'KD001', 1100, 500),
       ('WH01', '2018-06-06', 'KD001', 500, 0),
       ('WH01', '2018-06-07', 'KD001', 500, 800),
       ('WH01', '2018-06-08', 'KD001', 500, 0),
       ('WH01', '2018-06-09', 'KD001', 1000, 700),
       ('WH01', '2018-06-10', 'KD001', 800, 0);

• 每日库存=之前的库存日+ ORDERQTY- USEDQTY
• 但每月的第一个日期= STOCKMONTH + ORDERQTY- USEDQTY

我尝试了一些查询，但是没有得到正确的值。

WITH tmp_a AS
(
    SELECT 
        WH_CODE, 
        CONVERT(DATETIME,concat(MNTH,'01')) MNTH,
        MODELCODE, STOCKQTY 
    FROM 
        #Stock_Beginning
),
tmp_b AS  
(
    SELECT 
        a.WH_CODE, a.[DAY], a.MODELCODE, 
        ISNULL(b.STOCKQTY, 0) Beginning,
        a.USEDQTY, a.ORDERQTY, 
        ROW_NUMBER() OVER(PARTITION BY a.WH_CODE ORDER BY a.[DAY]) SEQ
    FROM 
        #WH_TRANS a
    LEFT OUTER JOIN 
        tmp_a b ON a.WH_CODE = b.WH_CODE
                AND a.MODELCODE = b.MODELCODE 
                AND a.[DAY] = b.MNTH
)
SELECT 
    WH_CODE, [DAY], 
    MODELCODE, BEGINNING,
    USEDQTY, ORDERQTY,
    CASE 
       WHEN SEQ = 1 THEN BEGINNING + ORDERQTY - USEDQTY
       ELSE LAG (BEGINNING + ORDERQTY - USEDQTY, 1, BEGINNING + ORDERQTY - USEDQTY) OVER (ORDER BY [DAY]) + ORDERQTY-USEDQTY 
    END AS ENDING 
FROM 
    tmp_b

结果看起来像这样：

我可以在查询中使用其他逻辑以获得所需结果吗？

请帮助

谢谢