How to update table field value in one table from field value in another table - sql

Question

I am trying to update field value from one table to another.
Item with bomRev='A' in Destination table look like show below
Same Item bomRev='A' in source table looks like
I want to update partid field in destination table for bomRev=A by the value in Source filed i want to destination looks exactly like the source.
I tried this but no luck
UPDATE [MIBOMD]
SET [MIBOMD].[partId] = [assy].[partId]
FROM [MIBOMD] INNER JOIN [assy] ON [MIBOMD].[partId] = [assy].[partId]
WHERE bomRev='A' and [bomItem]='600797' AND [MIBOMD].[partId]!=[assy].[partId];

Answer 1

UPDATE m
SET [partId] = a.[partId]
FROM
[MIBOMD] m
INNER JOIN
[assy] a
ON m.[bomItem] = a.[ItemId]
AND m.bomEntry = a.bomEntry
WHERE
m.bomRev='A'
AND m.[bomItem]='600797'
AND m.[partId]!=a.[partId];
You actually were pretty close! Just a couple of key differences. Before I explain I have used Table Aliases in the code I provided it is a shorthand way of referring to the table throughout the query that will make it a little easier to follow and read. To Alias a table after the table name in the from statement simply add a space and an alias or a space " AS " alias.
Now your Join as on partid in your version and that was your main issue. Because you want the records where partid are not the same so you can change the partid of the assy table. Looking at your dataset I was able to determine that the shared key was mibomd.bomItem and assy.ItemId. After clearing that up everything should be good.
Per your comment the only other thing that needed to be added was a second condition on the join to make it unique. [MIBOMD].bomEntry = assy.bomEntry
A little about join conditions. Typically you always want to figure out what the unique relationship between the 2 tables are (bomItem = ItemId and bomEntry = bomEntry) and that is what will go in the ON area of the join. Rarely that will be different and will be for very specific purposes.
Per your comment on how to insert the missing records
INSERT INTO MIBOMD (bomItem, bomRev, bomEntry, lineNbr, dType, partId)
SELECT
bomItem = a.ItemId
,bomRev = 'A' --or change the value to what you want
,a.bomEntry
,lineNbr = ???? --not sure how you are figure this out do if you wan it to be the next line number you can figure that out automatically if you need
,a.partId
FROM
assy a
LEFT JOIN MIBOMD m
ON a.ItemId = m.bomItem
AND a.bomEntry = m.bomEntry
WHERE
m.bomItem IS NULL
This time you would use a left join from assy to mibomd and figure out when they don't match mibomd.bomItem IS NULL