T-SQL for Updating Rows with same value in a column - sql-server

Question

I have a table lets say called FavoriteFruits that has NAME, FRUIT, and GUID for columns. The table is already populated with names and fruits. So lets say:
NAME FRUIT GUID
John Apple NULL
John Orange NULL
John Grapes NULL
Peter Canteloupe NULL
Peter Grapefruit NULL
Ok, now I want to update the GUID column with a new GUID (using NEWID()), but I want to have the same GUID per distinct name. So I want all the John Smiths to have the same GUID, and I want both the Peters to have the same GUID, but that GUID different than the one used for the Johns. So now it would look something like this:
NAME FRUIT GUID
John Apple f6172268-78b7-4c2b-8cd7-7a5ca20f6a01
John Orange f6172268-78b7-4c2b-8cd7-7a5ca20f6a01
John Grapes f6172268-78b7-4c2b-8cd7-7a5ca20f6a01
Peter Canteloupe e3b1851c-1927-491a-803e-6b3bce9bf223
Peter Grapefruit e3b1851c-1927-491a-803e-6b3bce9bf223
Can I do that in an update statement without having to use a cursor? If so can you please give an example?
Thanks guys...

Answer 1

Update a CTE won't work because it'll evaluate per row. A table variable would work:
You should be able to use a table variable as a source from which to update the data. This is untested, but it'll look something like:
DECLARE #n TABLE (Name varchar(10), Guid uniqueidentifier);
INSERT #n
SELECT Name, newid() AS Guid
FROM FavoriteFruits
GROUP BY Name;
UPDATE f
SET f.Guid = n.Guid
FROM #n n
JOIN FavoriteFruits f ON f.Name = n.Name
So that populates a variable with a GUID per name, then joins it back to the original table and updates accordingly.

Answer 2

To clarify comments re a table expression in the USING clause of a MERGE statement.
The following won't work because it'll evaluate per row:
MERGE INTO FavoriteFruits
USING (
SELECT NAME, NEWID() AS GUID
FROM FavoriteFruits
GROUP
BY NAME
) AS source
ON source.NAME = FavoriteFruits.NAME
WHEN MATCHED THEN
UPDATE
SET GUID = source.GUID;
But the following, using a table variable, will work:
DECLARE #n TABLE
(
NAME VARCHAR(10) NOT NULL UNIQUE,
GUID UNIQUEIDENTIFIER NOT NULL UNIQUE
);
INSERT INTO #n (NAME, GUID)
SELECT NAME, NEWID()
FROM FavoriteFruits
GROUP
BY NAME;
MERGE INTO FavoriteFruits
USING #n AS source
ON source.NAME = FavoriteFruits.NAME
WHEN MATCHED THEN
UPDATE
SET GUID = source.GUID;

Answer 3

There's a single-statement solution too, which, however, has some limitations. The idea is to use OPENQUERY(), like this:
UPDATE FavoriteFruits
SET GUID = n.GUID
FROM (
SELECT NAME, GUID
FROM OPENQUERY(
linkedserver,
'SELECT NAME, NEWID() AS GUID FROM database.schema.FavoriteFruits GROUP BY NAME'
)
) n
WHERE FavoriteFruits.NAME = n.NAME
This solution implies that you need to create a self-pointing linked server. Another specificity is that you can't use this method on table variables nor local temporary tables (global ones would do as well as 'normal' tables).