Comparing SQL and Prolog

Question

I\'ve started learning Prolog and wondering about the theoretical difference from the SQL language.

For example:

• both are declarative languages
• b

Answer 1

xonix, you need more development experience to say whether something can be done in sql or not.

Below are at least 2 solutions for your fibo series. One using Stored Procedure and the other using CTE. Take your pick.

METHOD 1

declare @a int, @b int, @c int, @i int, @N int = 10
select @a=0, @b=1, @i=0, @c=0
print @a
print @b
while @i < @N 
Begin
set @c=@a+@b
print @c
set @i=@i+1
set @a=@b
set @b=@c
end

METHOD 2

WITH FibonacciNumbers (RecursionLevel, FibonacciNumber, NextNumber) 
AS (
-- Anchor member definition
SELECT  
0  AS RecursionLevel,
0  AS FibonacciNumber,
1  AS NextNumber
UNION ALL
-- Recursive member definition
SELECT  a.RecursionLevel + 1             AS RecursionLevel,
a.NextNumber                     AS FibonacciNumber,
a.FibonacciNumber + a.NextNumber AS NextNumber
FROM FibonacciNumbers a
WHERE a.RecursionLevel < 10
)
-- Statement that executes the CTE
SELECT 
'F' + CAST( fn.RecursionLevel AS VARCHAR) AS FibonacciOrdinal, 
fn.FibonacciNumber,
fn.NextNumber
FROM FibonacciNumbers fn; 
GO

Answer 2

Just a few thoughts:

1. SQL is a query language for (maybe arbitrary complex) accessing to (relational) data, it's not a programming language.
2. Even if treat SQL as programming language - it's not Turing complete. I can hardly imagine sql query returning sum of 1 to 100 (for example).
3. SQL is language for accessing/manipulating (DML) to data bases, where Prolog is a language for working with knowledge bases (& rule resolution engine, of cause). Virtually Prolog is no more then simply unification & backtracking.
4. This is not saying about the application domains of SQL & Prolog, which are of cause totally different - efficient (regular) data storage & AI/symbolic computations/parsing/expert systems/constraint solvers/.../much more.