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I am currently watching this video on Entity Framework and about 15 minutes in, the speaker says that table value functions occasionally out perform UDF's.

My question is in what scenario do TVF's out perform UDF's?

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Didn't see the duplicate :/ my bad –  Stuart Blackler Dec 28 '11 at 14:29
    
There are two kinds of TVFs: inline and multi-statement. Typically inline ones perform well. –  A-K Jan 3 '12 at 4:19

2 Answers 2

up vote 7 down vote accepted
  • A scalar UDF with table access acts like a lookup inside a RBAR curso. That is, it executes once per row. And it's black box to the optimier
  • TVF is a macro that expands like a view and is consider part of the outer query

Scalar UDF have uses, but not in this case.

The performance difference can be huge: I've achived x100,000+ improvements by removing idiotic uses of UDFs

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+1, as for me the query ran 20 sec, after removing, yes - exactly - idiotic UDF, it ran 9 ms –  Oleg Dok Dec 28 '11 at 13:03

When do we need to call the function for every row - than in case of UDF it more looks like cursor loop - because it forces Sql Server to use single-threaded query plan. The TVF has no such restriction

So, the answer is - if the query CAN be parallelized - then TVF outperforms the UDF

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