Quicker way to update all rows in a SQL Server table

Question

Is there a more efficient way to write this code? Or with less code?

SELECT * 
INTO #Temp 
FROM testtemplate

Declare @id INT
Declare @name VARCHAR(127)

WHILE (SELECT Count(*) FROM #Temp) > 0 
BEGIN 

    SELECT TOP 1 @id = testtemplateid FROM #Temp
    SELECT TOP 1 @name = name FROM #Temp

    UPDATE testtemplate
    SET testtemplate.vendortestcode = (SELECT test_code FROM test_code_lookup WHERE test_name = @name)
    WHERE testtemplateid = @id

     --finish processing 
    DELETE #Temp Where testtemplateid = @id
END
DROP TABLE #Temp

Answer 1

You can do this in a single UPDATE with no need to loop.

UPDATE tt
    SET vendortestcode = tcl.test_code
    FROM testtemplate tt
        INNER JOIN test_code_lookup tcl
            ON tt.name = tcl.test_name

Answer 2

You could try a single update like this:

UPDATE A
SET A.vendortestcode = B.test_code
FROM testtemplate A
INNER JOIN test_code_lookup B
ON A.name = B.test_name

Also, the way you are doing it now is wrong, since you are taking a TOP 1 Id and a TOP 1 name in two separate querys, without an ORDER BY, so its not sure that you are taking the right name for your ID.

Answer 3

You could write a function to update vendortestcode. Then your code reduces to one SQL statement:

update testtemplate set vendortestcode = dbo.get_test_code_from_name(name)