Update Column using calculation in last year from another table - sql-server

Question

I am trying to update (using Inner joins for three tables) item stats STAT for table IM_ITEM by highlighting items that sold less than 12 as "D" (Discontinue).
The 2nd table PS_TKT_HIST_LIN has the Quantity sold column QTY_SOLD for each item on each day and the date column BUS_DAT.
I also need a third table IM_INV to filter the data, I need to say the last received date LST_RECV_DAT for these items is earlier than "2019-01-01" and last sales date LST_SAL_DAT is after "2019-01-01". I used the following code
UPDATE M
SET M.STAT = 'D'
FROM
dbo.IM_ITEM AS M
INNER JOIN
IM_INV AS N
ON
M.ITEM_NO = N.ITEM_NO
INNER JOIN
dbo.PS_TKT_HIST_LIN S`
ON
M.ITEM_NO = S.ITEM_NO
WHERE
CONVERT(DATETIME, FLOOR(CONVERT(FLOAT, N.LST_RECV_DAT))) <= '2019-01-01'
AND CONVERT(DATETIME, FLOOR(CONVERT(FLOAT, N.LST_SAL_DAT))) >= '2019-01-01'
AND M.STAT = 'A'
AND SUM(case when DATEPART(YYYY, (BUS_DAT)) = DATEPART(YYYY, DATEADD(YYYY, -1, getdate()))
AND DATEPART(yyyy, (BUS_DAT)) = DATEPART(yyyy, DATEADD(YYYY, -1, getdate()))
then qty_sold else 0)<12
It comes with an error
Any advise please

Answer 1

You should use HAVING clause instead of Sum in where.
You can use CTE to achieve the value, then update accordingly.
;with cte as(
select ITEM_NO, ..
from ..
group by ITEM_NO
having .. < 12
)
update M
set SET M.STAT = 'D'
from dbo.IM_ITEM AS M
inner join cte on M.ITEM_NO = cte.ITEM_NO

Answer 2

You can't use an aggregate function in where clause unless defined under subquery.