SELECT
    cdd.NumeroIdentificacion ,
    cdd.Prestamos ,
    CAST(REPLACE(cdd.Prestamos,',','.') AS FLOAT) * 100 /( SELECT
                SUM(CAST(REPLACE(cdd.Prestamos,',','.') AS FLOAT))
          FROM
            CentralDeDeudores AS a
          WHERE
            a.NumeroIdentificacion = cdd.NumeroIdentificacion
            GROUP BY
            a.NumeroIdentificacion
        ) AS porcentaje

FROM
    CentralDeDeudores cdd


GROUP BY
    cdd.NumeroIdentificacion,cdd.Prestamos

SELECT  T1.NumeroIdentificacion ,
        T1.Prestamos/T2.TotalPrestamos
        FROM CentralDeDeudores T1
    INNER JOIN (    SELECT  NumeroIdentificacion ,
                    SUM(Prestamos)  AS 'TotalPrestamos'
                    FROM CentralDeDeudores
                GROUP BY
                    NumeroIdentificacion
        ) T2
        ON T2.NumeroIdentificacion = T1.NumeroIdentificacion