using scalar function output in an update

Suppose I have a 2 column table with columns (arg, value) and a user-defined functi开发者_如何学JAVAon foo.

Is there a way to have an update query that goes through the table and calls foo with argument arg and sticks the results in column value for every row in the table?

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Assuming SQL Server the syntax is

Update YourTable
SET value = dbo.foo(arg)

It is often more efficient to not use scalar UDFs for Row by Row processing however. What is the scalar UDF doing?