Oracle 18c

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CREATE FUNCTION GCD(
  a IN NUMBER,
  b IN NUMBER
) RETURN NUMBER DETERMINISTIC
IS
BEGIN
  IF b = 0 THEN
    RETURN a;
  ELSE
    RETURN GCD(b,MOD(a,b));
  END IF;
END;
/
CREATE FUNCTION LCM(
  a IN NUMBER,
  b IN NUMBER
) RETURN NUMBER DETERMINISTIC
IS
BEGIN
  RETURN (a*b)/GCD(a,b);
END;
/
CREATE TYPE LCMAggregationType AS OBJECT(
  value NUMBER,

  STATIC FUNCTION ODCIAggregateInitialize(
    ctx         IN OUT LCMAggregationType
  ) RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateIterate(
    self        IN OUT LCMAggregationType,
    value       IN     NUMBER
  ) RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateTerminate(
    self        IN OUT LCMAggregationType,
    returnValue    OUT NUMBER,
    flags       IN     NUMBER
  ) RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateMerge(
    self        IN OUT LCMAggregationType,
    ctx         IN OUT LCMAggregationType
  ) RETURN NUMBER
);
/
CREATE OR REPLACE TYPE BODY LCMAggregationType
IS
  STATIC FUNCTION ODCIAggregateInitialize(
    ctx         IN OUT LCMAggregationType
  ) RETURN NUMBER
  IS
  BEGIN
    ctx := LCMAggregationType( 1 );
    RETURN ODCIConst.SUCCESS;
  END;

  MEMBER FUNCTION ODCIAggregateIterate(
    self        IN OUT LCMAggregationType,
    value       IN     NUMBER
  ) RETURN NUMBER
  IS
  BEGIN
    IF value IS NOT NULL THEN
      self.value := LCM( self.value, value );
    END IF;
    RETURN ODCIConst.SUCCESS;
  END;

  MEMBER FUNCTION ODCIAggregateTerminate(
    self        IN OUT LCMAggregationType,
    returnValue    OUT NUMBER,
    flags       IN     NUMBER
  ) RETURN NUMBER
  IS
  BEGIN
    returnValue := self.value;
    RETURN ODCIConst.SUCCESS;
  END;

  MEMBER FUNCTION ODCIAggregateMerge(
    self        IN OUT LCMAggregationType,
    ctx         IN OUT LCMAggregationType
  ) RETURN NUMBER
  IS
  BEGIN
    self.value := LCM( self.value, ctx.value );
    RETURN ODCIConst.SUCCESS;
  END;
END;
/
CREATE FUNCTION LCM_AGG( value NUMBER )
RETURN NUMBER
PARALLEL_ENABLE AGGREGATE USING LCMAggregationType;
/
CREATE TABLE table_name ( id, group_id, numerator, denominator ) AS
SELECT 1, 13,  4,  12 FROM DUAL UNION ALL
SELECT 2, 13, 33, 126 FROM DUAL UNION ALL
SELECT 3, 13,  8,  45 FROM DUAL UNION ALL
SELECT 4, 28, 56, 137 FROM DUAL UNION ALL
SELECT 5, 28, 13, 236 FROM DUAL UNION ALL
SELECT 6, 28, 69, 145 FROM DUAL;
6 rows affected

SELECT group_id,
       SUM( numerator ) AS numerator,
       MAX( denominator ) AS denominator
FROM   (
  SELECT group_id,
         numerator * LCM_AGG( denominator ) OVER ( PARTITION BY group_id ) / denominator
           AS numerator,
         LCM_AGG( denominator ) OVER ( PARTITION BY group_id ) as denominator
  FROM   table_name
)
GROUP BY group_id;


GROUP_ID
NUMERATOR
DENOMINATOR


13
974
1260

28
4405473
4688140