查询：

select sum(billamt) from SALES group by DATE,RNAME

返回按DATE,RNAME分组的billamt的sum。
如果有多个DATE或RNAME唯一值，则返回值是一个表（而不是一个字段）。
可以单独运行此查询并检查返回值。
如错误所述，不能为一个字段设置多个值。

尝试以下内容：

update A
set Total = B.Total
From tableA  A
Inner Join (select DATE,RNAME,sum(billamt) Total from SALES group by DATE,RNAME) B
On A.Date = B.Date and A.RName = B.RNAme

由于在上面的问题中表的结构不清楚，我假设tableA有列Total、Date和RName

update tableA set tableA.total = 
a.total from (select SUM(amt) as total, date, rname from SALES group by DATE,RNAME) as a
where a.date = tableA.date and tableA.rname = a.rname

--编辑“销售表中Rname可以为空的情况”使用

update tableA set tableA.total = a.total
from (select SUM(amt) as total, date, rname from #t1 group by DATE,RNAME) as a
where a.date = tableA.date and tableA.rname = a.rname
OR (a.date = tableA.date AND tableA.rname IS NULL and a.rname IS NULL)

--进一步阐述

CREATE TABLE #t1 (amt decimal(18,2), [date] date, rname varchar(50))
INSERT INTO #t1
SELECT 1.9, GETDATE() - 1, NULL
UNION ALL
SELECT 1.9, GETDATE() - 1, NULL
UNION ALL
SELECT 8.9, GETDATE() - 1, NULL
UNION ALL
SELECT 8.9, GETDATE(), NULL
UNION ALL
SELECT 2.9, GETDATE() - 1, 'N1'
UNION ALL
SELECT 2.8, GETDATE() - 1, 'N1'

CREATE TABLE #t2 (total decimal(18,2), [date] date, rname varchar(50))
INSERT INTO #t2
SELECT 0, GETDATE() - 1, NULL
UNION ALL
SELECT 0, GETDATE() - 1, 'N1'

update #t2 set #t2.total = a.total
from (select SUM(amt) as total, date, rname from #t1 group by DATE,RNAME) as a
where a.date = #t2.date and #t2.rname = a.rname
OR (a.date = #t2.date AND #t2.rname IS NULL and a.rname IS NULL)

SELECT * FROM #t2

我希望现在一切都清楚了