in reply to Re:x3 How NOT to do it
in thread How NOT to do it

But note that SQL is pretty unusual. For instance how many other programming languages do you know which, by design, are not Turing complete?

Brownie points to the first person who can say why it is very important that SQL not be a Turing complete language. :-)

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Re: Re (tilly) 4: How NOT to do it
by Louis_Wu (Chaplain) on Sep 11, 2003 at 05:11 UTC
    Since no one has answered your challenge in 2 years, I'll ask:
    Why is it very important that SQL not be a Turing complete language?
    The only answer^W guess I can come up with is the rhetorical - imagine someone trying to code an OS or any complete program in a database. But I don't really know. Thanks.

    Perl programming and scheduling in the corporate world, as explained by dragonchild:
    "Uhh ... that'll take me three weeks, broken down as follows: 1 day for coding, the rest for meetings to explain why I only need 1 day for coding."
[reply]
      Sorry for being slow getting back, I have been offline.

      The answer is that the database is supposed to figure out exactly what the SQL is supposed to do, and then come up with a very efficient way to do that. With a Turing-complete language it is impossible to answer detailed questions about arbitrary code, and is difficult to answer them even for normal code.

      Sure, optimizers can speed up code. But in a normal language they can't recognize a bad algorithm and rewrite it with a more efficient one. But SQL routinely is optimized to be using algorithms which are far better than any that the developer would have thought up.

      SQL could not do this if the developer had, for instance, the freedom to write a series of nested loops with possibly relevant side-effects and a difficult to discern purpose.

[reply]

      It's that queries cannot be recursive. Of course, there have been a number of papers popping up here and there about Turing-complete SQL extensions.

      antirice    
      The first rule of Perl club is - use Perl
      The       ith rule of Perl club is - follow rule i - 1 for i > 1

[reply]
        It's that queries cannot be recursive. Of course, there have been a number of papers popping up here and there about Turing-complete SQL extensions.
        I can see how recursive queries could get rediculous, but why prevent that ability? Is it dangerous? Does it violate DB 'best practices'?

        I don't know much of anything about DB internals, or even the interfaces, so I'm groping here.

        *sigh* I just used a PHBism. Where's that lobotamy brochure?

        Perl programming and scheduling in the corporate world, as explained by dragonchild:
        "Uhh ... that'll take me three weeks, broken down as follows: 1 day for coding, the rest for meetings to explain why I only need 1 day for coding."
[reply]

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