UPDATE column from one table to another - tsql

Question

I need to update a column in a table to the latest date/time combination from another table. How can I get the latest date/time combination from the one table and then update a column with that date in another table?
The two tables I am using are called dbo.DD and dbo.PurchaseOrders. The JOIN between the two tables are dbo.DueDate.XDORD = dbo.PurchaseOrders.PBPO AND dbo.DueDate.XDLINE = dbo.PurchaseOrders.PBSEQ. The columns from dbo.DueDate that I need the latest date/time from are dbo.DueDate.XDCCTD and dbo.DueDate.XDCCTT.
I need to set dbo.PurchaseOrders.PBDUE = dbo.DueDate.XDCURDT.I can't use an ORDER BY statement in the UPDATE statement, so I'm not sure how to do this. I know row_number sometimes works in these situations, but I'm unsure of how to implement.

Answer 1

The general pattern is:
;WITH s AS
(
SELECT
key, -- may be multiple columns
date_col,
rn = ROW_NUMBER() OVER
(
PARTITION BY key -- again, may be multiple columns
ORDER BY date_col DESC
)
FROM dbo.SourceTable
)
UPDATE d
SET d.date_col = s.date_col
FROM dbo.DestinationTable AS d
INNER JOIN s
ON d.key = s.key -- one more time, may need multiple columns here
WHERE s.rn = 1;
I didn't try to map your table names and columns because (a) I didn't get from your word problem which table was the source and which was the destination and (b) those column names look like alphabet soup and I would have screwed them up anyway.
Did seem though that the OP got this specific code working:
;WITH s AS
(
SELECT
XDORD, XDLINE,
XDCURDT,
rn = ROW_NUMBER() OVER
(
PARTITION BY XDORD, XDLINE
ORDER BY XDCCTD DESC, XDCCTT desc
)
FROM dbo.DueDate
)
UPDATE d
SET d.PBDUE = s.XDCURDT
FROM dbo.PurchaseOrders AS d
INNER JOIN s
ON d.PBPO = s.XDORD AND d.PBSEQ = s.XDLINE
WHERE s.rn = 1;