Query for updating a column in same table from same table - sql

Question

I have to update the authorid column which are matching (where documentculture = 'en-US'
to matching (where documentculture = 'el-GR' in the same table. which includes a inner join to another table
I written like below which looks wrong:
UPDATE t1
SET t1.authorid = t2.authorid
FROM wv_blogdata AS t1
INNER JOIN wv_blogdata AS t2
ON t1.documentnodeid = t2.documentnodeid
inner join CMS_Document d
ON d.BlogDataID = d.DocumentForeignKeyValue
WHERE t2.DocumentCulture = 'en-US';
could you please correct me?
More explanation:
select authorid from wv_blogdata
inner join CMS_Document
on wv_blogdata.BlogDataID = CMS_Document.DocumentForeignKeyValue
Where DocumentCulture ='el-GR'
The author id of above query is different from authorid of below query
which i want to make it synch
select authorid from wv_blogdata
inner join CMS_Document
on wv_blogdata.BlogDataID = CMS_Document.DocumentForeignKeyValue
Where DocumentCulture ='en-US'

Answer 1

As Zohar Peled says in the comments, unless you give sample data, expected results as well as your current DML it's hard to produce an accurate answer to your question.
That being said, in general terms if you can produce a select statement using table aliases that shows both the field to be updated and the field with the new value then you can use it as the basis for a successful UPDATE query.
So if the correct results are shown in this query(your original converted into a SELECT):
SELECT t1.authorid AS OldValue, t2.authorid AS NewValue
FROM wv_blogdata AS t1
INNER JOIN wv_blogdata AS t2
ON t1.documentnodeid = t2.documentnodeid
INNER JOIN CMS_Document d
ON d.BlogDataID = d.DocumentForeignKeyValue
WHERE t2.DocumentCulture = 'en-US';
you will get the correct outcome from this query(your original):
UPDATE t1
SET t1.authorid = t2.authorid
FROM wv_blogdata AS t1
INNER JOIN wv_blogdata AS t2
ON t1.documentnodeid = t2.documentnodeid
INNER JOIN CMS_Document d
ON d.BlogDataID = d.DocumentForeignKeyValue
WHERE t2.DocumentCulture = 'en-US';
Remembering of course to test your work for unexpected outcomes and hidden gotchas.
Again without sufficient sample data it's really hard to give you a definitive answer, so include as much detail as possible to help us help you.
Hope this helps you to work it out.

Answer 2

The following query should make the records in sync so authorid of german blogs and authorid of usa blogs will become the same after you run this query.
Note that top(1) is required so only one value is returned by the sub-query else if there are multiple blog records for german culture you will encounter an error.
UPDATE b
SET b.authorid =
(SELECT top(1) wvb.authorid
FROM wv_blogdata wvb
INNER JOIN CMS_Document cms ON wvb.BlogDataID = cms.DocumentForeignKeyValue
WHERE cms.DocumentCulture ='el-GR' AND b.BlogDataID = cms.DocumentForeignKeyValue order by wvb.authorid)
FROM wv_blogdata b
INNER JOIN CMS_Document ON b.BlogDataID = CMS_Document.DocumentForeignKeyValue
WHERE CMS_Document.DocumentCulture ='en-US';