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Fri, Jun 3 2011 12:40 PM | Permanent Link |
Tim Young [Elevate Software] Elevate Software, Inc. ![]() | Roy,
<< Fascinating. I'm especially gobsmacked by the fact that a generated column can use the function but a computed one can't. I hadn't realised there was a difference or if Tim had told me I'd forgotten. >> COMPUTED columns are re-computed client-side for remote sessions/client-server, and they don't have access to the database catalog for resolving user-defined functions. Therefore, they can only use the built-in functions in the engine. GENERATED columns are re-generated on INSERT/UPDATE at the server-side, so they have complete access to the database catalog. You can test this by doing the following: SELECT Column1+Column2 AS ComputedExpression, MyUDF(Column1) AS GeneratedExpression FROM MyTable Make sure to request a sensitive result set, and then view the differences in how the two expressions are re-computed when you modify Column1. The ComputedExpression will update in real-time as you modify Column1, whereas the GeneratedExpression will only change once you post any modifications. -- Tim Young Elevate Software www.elevatesoft.com |
Fri, Jun 3 2011 1:55 PM | Permanent Link |
Roy Lambert NLH Associates ![]() | Tim
Reading it I think I've seen that explanation before. I'm sure that at some point it, like many other things, will finally sink in. Roy Lambert |
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