3 ms·

Is SQL a declarative language? It requires predicates for everything. Even declaring a schema requires a predicate, which doesn't seem any different than functi

Is SQL a declarative language? It requires predicates for everything. Even declaring a schema requires a predicate, which doesn't seem any different than function arguments to me. "select" abstracting the underlying DB engine's "control flow" doesn't seem characteristically declarative. It seems like the same type of standard library that any imperative language would offer for convenience. Edit: Apparently functional programming is declarative.

empath75 8y ago
If it's not, then nothing is.
- deckar01 8y ago
  Apparently functional programming is considered a form of declarative programming. That doesn't make much sense to me, but I guess relative to writing assembly or C it is declarative. The distinction seems arbitrary, because even C and assembly contain abstractions for more complex operations taking place in the OS and in the hardware.
  - deleted 8y ago
    [deleted]
  - taffer 8y ago
    The difference is referential transparency: In declarative programming, an expression always returns the same result, no matter where and in which order you use it. Contrast this with an expression like a += 1; in C, which returns a different result each time.
  - rgoulter 8y ago
    A cliche example is "squares of values". imperative code would be something like: fn squares(array A) array B; for (idx, x) in A { B[idx] = x * x } return B; } (or "B.add" or some other mutating action). whereas 'declarative' code 'declares' what it wants: fn squares(array A) { return A.map { |x| x * x } } I think "declarative" is used more in terms of "declare the result you want, not how you'll get it". It's easier to focus on what the output of the program is with declarative code. Higher-level abstractions are probably necessary, but I don't think it's fundamental to how I'd use the term. :-) Although I wouldn't be surprised to see a variety of ways people use the term.
    - jtms 8y ago
      Is that example code elixir?
      - rgoulter 8y ago
        It's not anything in particular. Rosetta Code has "apply a callback to an array" example with Elixir. https://rosettacode.org/wiki/Apply_a_callback_to_an_array#Elixir https://rosettacode.org/wiki/Apply_a_callback_to_an_array#El... Enum.map([1, 2, 3], fn(n) -> n * 2 end) Enum.map [1, 2, 3], &(&1 * 2)
swsieber 8y ago
It is declarative. The db does th query planning, not you. E.g. you don't tell the db whether to do a full row scan or an index scan.
ako 8y ago
Yes, as the predicate defines what you want it to do, not how. The database engine will transform your declared goal into an execution plan (query plan), which defines how it will achieve what you want.
jVinc 8y ago
You can't just blankly state that functional programming is or isn't declarative. sort([42,7,2]) is declarative in that it declares what is wanted not how to do it. But if you write a functional bubble-sort, then that function is not a declaration of intent its a functional reimplementation of a method. Now naturally if your write a Haskel SQL parser/query planner and executor, then you can have a functional implementation of a program that executes a declarative language. And you could easily make a subset of haskel commands that declare your query in a functional manor then, instead of parsing SQL, and that subset, or DSL would be a declarative query language. That does not however make Haskel a declarative language overall. Long story short, an orange isn't a weapon in general, but you can make it into one in specific cases.

empath75 8y ago

If it's not, then nothing is.

deckar01 8y ago
Apparently functional programming is considered a form of declarative programming. That doesn't make much sense to me, but I guess relative to writing assembly or C it is declarative. The distinction seems arbitrary, because even C and assembly contain abstractions for more complex operations taking place in the OS and in the hardware.
- deleted 8y ago
  [deleted]
- taffer 8y ago
  The difference is referential transparency: In declarative programming, an expression always returns the same result, no matter where and in which order you use it. Contrast this with an expression like a += 1; in C, which returns a different result each time.
- rgoulter 8y ago
  A cliche example is "squares of values". imperative code would be something like: fn squares(array A) array B; for (idx, x) in A { B[idx] = x * x } return B; } (or "B.add" or some other mutating action). whereas 'declarative' code 'declares' what it wants: fn squares(array A) { return A.map { |x| x * x } } I think "declarative" is used more in terms of "declare the result you want, not how you'll get it". It's easier to focus on what the output of the program is with declarative code. Higher-level abstractions are probably necessary, but I don't think it's fundamental to how I'd use the term. :-) Although I wouldn't be surprised to see a variety of ways people use the term.
  - jtms 8y ago
    Is that example code elixir?
    - rgoulter 8y ago
      It's not anything in particular. Rosetta Code has "apply a callback to an array" example with Elixir. https://rosettacode.org/wiki/Apply_a_callback_to_an_array#Elixir https://rosettacode.org/wiki/Apply_a_callback_to_an_array#El... Enum.map([1, 2, 3], fn(n) -> n * 2 end) Enum.map [1, 2, 3], &(&1 * 2)

swsieber 8y ago

It is declarative. The db does th query planning, not you. E.g. you don't tell the db whether to do a full row scan or an index scan.

ako 8y ago

Yes, as the predicate defines what you want it to do, not how. The database engine will transform your declared goal into an execution plan (query plan), which defines how it will achieve what you want.

jVinc 8y ago

You can't just blankly state that functional programming is or isn't declarative. sort([42,7,2]) is declarative in that it declares what is wanted not how to do it. But if you write a functional bubble-sort, then that function is not a declaration of intent its a functional reimplementation of a method. Now naturally if your write a Haskel SQL parser/query planner and executor, then you can have a functional implementation of a program that executes a declarative language. And you could easily make a subset of haskel commands that declare your query in a functional manor then, instead of parsing SQL, and that subset, or DSL would be a declarative query language. That does not however make Haskel a declarative language overall. Long story short, an orange isn't a weapon in general, but you can make it into one in specific cases.