Re: Imperative Query Languages

[Jason Dusek <jason.dusek@xxxxxxxxx>]

On Tue, 4 Jul 2017 at 23:57 Chris Travers chris.travers@xxxxxxxxx wrote:

I am curious where you see LINQ as starting at an imperative syntax.

The imperative integration is thin, I admit — it just the integration with for loops.

Here's a good case that illustrates the problem I think.  Suppose the following is understood imperatively:

FOR x IN RANGE student

SELECT WHERE x.age < 25

PROJECT ALL(x), lock_if_possible(x.id)

Now, lock_if_possible has side effects.  If we understand this to be imperative, then we have no possibility of turning this into a declarative query because we are interested in the side effects.  So you cannot say that this is equivalent to the SQL of

SELECT *, lock_if_possible(id)

FROM student

WHERE age < 25

The reason is that while the imperative version represents *one* valid interpretation of the declarative, there are other interpretations of the declarative that are not at all equivalent.  The hoops we have to jump through to make this work in an imperative way in SQL are sometimes rather amusing.

What are some alternative interpretations of this query? Are you referring to which rows are candidates for locking? Or the order of locking?

Kind Regards,

Jason

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