Question

I want to convert a table storing in Name-Value pair data to relational form in SQL Server 2008.

Source table

Strings
ID  Type    String
100 1   John
100 2   Milton
101 1   Johny
101 2   Gaddar

Target required

Customers
ID  FirstName   LastName
100 John        Milton
101 Johny       Gaddar

I am following the strategy given below,

Populate the Customer table with ID values in Strings Table

INSERT INTO CUSTOMERS SELECT DISTINCT ID FROM Strings

You get the following

Customers
ID  FirstName   LastName
100 NULL        NULL
101 NULL        NULL

Update Customers with the rest of the attributes by joining it to Strings using ID column. This way each record in Customers will have corresponding 2 matching records.

UPDATE Customers
    SET FirstName = (CASE WHEN S.Type=1 THEN S.String ELSE FirstName)
        LastName = (CASE WHEN S.Type=2 THEN S.String ELSE LastName)
FROM Customers
    INNER JOIN Strings ON Customers.ID=Strings.ID

An intermediate state will be llike,

ID  FirstName   LastName    ID  Type    String
100 John        NULL        100 1   John
100 NULL        Milton      100 2   Milton
101 Johny       NULL        101 1   Johny
101 NULL        Gaddar      101 2   Gaddar

But this is not working as expected. Because when assigning the values in the SET clause it is setting only the committed values instead of the uncommitted. Is there anyway to set uncommitted values (with in the processing time of query) in UPDATE statement?

PS: I am not looking for alternate solutions but make my approach work by telling SQL Server to use uncommitted data for UPDATE.

Answer 1

Have a look at this, it should avoid all the steps you had

DECLARE @Table TABLE(
        ID INT,
        Type INT,
        String VARCHAR(50)
)
INSERT INTO @Table (ID,[Type],String) SELECT 100 ,1   ,'John'
INSERT INTO @Table (ID,[Type],String) SELECT 100 ,2   ,'Milton'
INSERT INTO @Table (ID,[Type],String) SELECT 101 ,1   ,'Johny'
INSERT INTO @Table (ID,[Type],String) SELECT 101 ,2   ,'Gaddar'

SELECT  IDs.ID,
        tName.String NAME,
        tSur.String Surname
FROM    (
            SELECT DISTINCT ID
            FROM @Table
        ) IDs LEFT JOIN
        @Table tName ON IDs.ID = tName.ID AND tName.[Type] = 1  LEFT JOIN
        @Table tSur ON IDs.ID = tSur.ID AND tSur.[Type] = 2

OK, i do not think that you will find a solution to what you are looking for. From UPDATE (Transact-SQL) it states

Using UPDATE with the FROM Clause

The results of an UPDATE statement are
undefined if the statement includes a
FROM clause that is not specified in
such a way that only one value is
available for each column occurrence
that is updated, that is if the UPDATE
statement is not deterministic. For
example, in the UPDATE statement in
the following script, both rows in
Table1 meet the qualifications of the
FROM clause in the UPDATE statement;
but it is undefined which row from
Table1 is used to update the row in
Table2.

USE AdventureWorks;
GO
IF OBJECT_ID ('dbo.Table1', 'U') IS NOT NULL
    DROP TABLE dbo.Table1;
GO
IF OBJECT_ID ('dbo.Table2', 'U') IS NOT NULL
    DROP TABLE dbo.Table2;
GO
CREATE TABLE dbo.Table1 
    (ColA int NOT NULL, ColB decimal(10,3) NOT NULL);
GO
CREATE TABLE dbo.Table2 
    (ColA int PRIMARY KEY NOT NULL, ColB decimal(10,3) NOT NULL);
GO
INSERT INTO dbo.Table1 VALUES(1, 10.0), (1, 20.0), (1, 0.0);
GO

UPDATE dbo.Table2 
SET dbo.Table2.ColB = dbo.Table2.ColB + dbo.Table1.ColB
FROM dbo.Table2 
    INNER JOIN dbo.Table1 
    ON (dbo.Table2.ColA = dbo.Table1.ColA);
GO
SELECT ColA, ColB 
FROM dbo.Table2;