Aggregate function not allowed in Set statment in TSQL - sql-server

Question

I need to update one table with values from another table (msdb.dbo.sysjobhistory). Since I need to get the max values of the run_time and run_date, I kept getting 'aggregate function not allowed in set statement' error. As a workaround, I tried the following but something isn't right because ALL the values in every row are the same, indicating either an error in the join or something I can't figure out.This is what I have (which is not correct):
UPDATE inventory.dbo.books SET
auth_time = t1.at,
auth_date = t1.ad
FROM (SELECT MAX(run_time) AS at, MAX(run_date) AS ad
FROM msdb.dbo.sysjobhistory h
INNER JOIN inventory.dbo.books t
ON h.job_id = t.jobid) t1
ALSO, I need to be able to convert the run_time into decimal(10,2) format (as the auth_time field is that) and run_date into datetime (as auth_time is datetime format).

Answer 1

You're so close!
Just move your subquery reference from the From Clause to a subquery in the Set for each field.
Try this:
UPDATE inventory.dbo.books SET
auth_time = (SELECT MAX(run_time)
FROM msdb.dbo.sysjobhistory h
INNER JOIN inventory.dbo.books t
ON h.job_id = t.jobid)
, auth_date = (SELECT MAX(run_date)
FROM msdb.dbo.sysjobhistory h
INNER JOIN inventory.dbo.books t
ON h.job_id = t.jobid);
The subquery in the SET for each field essentially returns a single value when the subquery is executed. Therefore, the use of a subquery doesn't break any of the rules of the set operation.
If your logic starts getting too complicated and your set fields too numerous to want to repeat everything as a subquery for each field, then you can also use a CTE.
With CTE as (
Select MAX(run_time) as at
, MAX(run_date) as ad
FROM msdb.dbo.sysjobhistory h
INNER JOIN inventory.dbo.books t
ON h.job_id = t.jobid
)
Update #Temp
Set auth_time = CTE.at
, auth_date = CTE.ad
From CTE
Let me know if you have any questions!

Answer 2

You can join to a subquery.
And in that subquery you're allowed to use group by.
Then do the casts or converts when the destination fields are set.
For example:
UPDATE b
SET
auth_time = left(replace(cast(h.max_run_time as varchar),':',''),8),
auth_date = cast(h.max_run_date as datetime)
FROM inventory.dbo.books b
JOIN (
select
job_id,
max(run_time) as max_run_time,
max(run_date) as max_run_date
from msdb.dbo.sysjobhistory
group by job_id
) h
ON (b.job_id = h.job_id);
I didn't know what kind of number is expected in that auth_time.
So the max_run_time is just converted from a TIME to a VARCHAR.
The varchar is implicitly converted to the DECIMAL of the destination field.
For example: time '12:15:25.0000000' --> decimal(10,2) 121525.00