Initial data commit

Task/Greatest-common-divisor/Transact-SQL/greatest-common-divisor.sql

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+CREATE OR ALTER FUNCTION [dbo].[PGCD]
+    (    @a BigInt
+    ,    @b BigInt
+    )
+RETURNS BigInt
+WITH RETURNS NULL ON NULL INPUT
+-- Calculates the Greatest Common Denominator of two numbers (1 if they are coprime).
+BEGIN
+DECLARE @PGCD BigInt;
+
+WITH    Vars(A, B)
+As  (   SELECT  Max(V.N) As A
+            ,   Min(V.N) As B
+        FROM (  VALUES  ( Abs(@a) , Abs(@b)) ) Params(A, B)
+        -- First, get absolute value
+        Cross APPLY (   VALUES (Params.A) , (Params.B) ) V(N)
+        -- Then, order parameters without Greatest/Least functions
+        WHERE Params.A > 0
+            And Params.B > 0 -- If 0 passed in, NULL shall be the output
+    )
+    ,   Calc(A, B)
+As  (   SELECT  A
+            ,   B
+        FROM    Vars
+
+        UNION ALL
+
+        SELECT  B As A
+            ,   A % B As B -- Self-ordering
+        FROM    Calc
+        WHERE   Calc.A > 0
+            And Calc.B > 0
+    )
+SELECT  @PGCD = Min(A)
+FROM    Calc
+WHERE   Calc.B = 0
+;
+
+RETURN @PGCD;
+
+END