Update from Temp Table

Question

Query:

SELECT ID, T.c.value('@Address', 'nvarchar(20)' ) as Address
INTO #TMP
FROM TABLE1
    CROSS APPLY XMLData.nodes('/Document') AS T(c)

UPDATE TABLE1
SET HomeAddress = (SELECT TOP 1 t.Address
                   FROM #TMP t
                   WHERE t.ID = ID)

Mainly, I need to copy data OUT from an XML field to normal fields within the same table.

Questions:

1. Any reason why all the records get the HomeAddress on Table1?
2. Is really Cursor the only way to update the value on Table1?

Answer 1

On the update, I need to FULLY QUALIFY the Table as follow:                  

UPDATE TABLE1 SET TABLE1.HomeAddress = (SELECT TOP 1 t.Address  
               FROM #TMP t  
               WHERE t.ID = TABLE1.ID)  

Answer 2

UPDATE T2
SET HomeAddress = t1.address
FROM TABLE2 t2
join TABLE1 t1 on T1.ID = t2.HomeAddressID
and t2.HomeAddress <> t1.address

Use a join. No need to temp table or correlated subquery.

If table 1 is in a one to many relationshisp these are some posibilites for handling that. If you havea value that indicates one and only one record (we have a field in our system that picks the most important address, it is maintained with a trigger to guarantee uniquesness), the try this:

UPDATE T2
SET HomeAddress = t1.address
FROM TABLE2 t2
join TABLE1 t1 on t1.ID = t2.HomeAddressID
WHERE t1.somefield = 'somevalue'
and t2.HomeAddress <> t1.address

If you need to based the unique record on asome other field (such as the most recent date), then try a variation of this:

UPDATE T2
SET HomeAddress = t1.address
FROM TABLE2 t2
join TABLE1 t1 on t1.ID = t2.HomeAddressID
join (select id, max(somedatefield) from  table1 group by id) t3 on t3.id = t1.id
Where  t2.HomeAddress <> t1.address