我有一个表t，其中包含date, ticker, open, high, low, close列。
declare @t table
(
[Datecol] date,
Ticker varchar(10),
[open] decimal (10,2),
[high] decimal (10,2),
[low] decimal (10,2),
[close] decimal(10,2)
)
insert into @t values
('20180215', 'ABC', '122.01', '125.76', '118.79' , '123.29')
,('20180216', 'ABC', '123.02', '130.62', '119.94' , '128.85')
,('20180217', 'ABC', '131.03', '139.80', '129.42' , '136.75')
,('20180218', 'ABC', '136.40', '137.95', '124.32' , '127.38')
,('20180219', 'ABC', '127.24', '138.52', '126.70' , '137.47')
,('20180220', 'ABC', '137.95', '142.01', '127.86' , '128.36')
,('20180215', 'JKL', '9.94', '10.30', '9.77' , '10.17')
,('20180216', 'JKL', '10.15', '10.24', '9.70' , '10.02')
,('20180217', 'JKL', '10.01', '10.18', '9.93' , '10.15')
,('20180218', 'JKL', '10.16', '10.20', '9.23' , '9.38')
,('20180219', 'JKL', '9.37', '9.79', '9.36' , '9.68')
,('20180220', 'JKL', '9.69', '10.01', '9.26' , '9.28')
我有兴趣计算每个股票代码的每日平均真实范围（ATR）。
ATR = Max（今日高位，昨日收盘价） - 最低价（今日低点，昨日收盘价）
使用LAG功能，我可以在昨天结束：
SELECT
*,
((LAG([close], 1) OVER (PARTITION BY Ticker ORDER BY [Datecol])) - 0) * 1 AS 'yest_close'
FROM
@t t
Datecol Ticker open high low close yest_close
--------------------------------------------------------------
2018-02-15 ABC 122.01 125.76 118.79 123.29 NULL
2018-02-16 ABC 123.02 130.62 119.94 128.85 123.29
2018-02-17 ABC 131.03 139.80 129.42 136.75 128.85
2018-02-18 ABC 136.40 137.95 124.32 127.38 136.75
2018-02-19 ABC 127.24 138.52 126.70 137.47 127.38
2018-02-20 ABC 137.95 142.01 127.86 128.36 137.47
2018-02-15 JKL 9.94 10.30 9.77 10.17 NULL
2018-02-16 JKL 10.15 10.24 9.70 10.02 10.17
2018-02-17 JKL 10.01 10.18 9.93 10.15 10.02
2018-02-18 JKL 10.16 10.20 9.23 9.38 10.15
2018-02-19 JKL 9.37 9.79 9.36 9.68 9.38
2018-02-20 JKL 9.69 10.01 9.26 9.28 9.68
我如何获得最大值（今天的高点，昨天的收盘价）？