Filtra empresas com historico completo, e calcula o sinal acumulado.

cumulative_sum.hql

DROP TABLE IF EXISTS temp1;

CREATE TABLE temp1 (anomes INT, cnpj STRING, x DOUBLE);

INSERT INTO temp1 VALUES
  (201801, 'c0', 1),
  (201801, 'c1', 1),
  (201801, 'c2', 3),
  (201802, 'c0', 2),
  (201802, 'c1', 2),
  (201802, 'c2', null),
  (201803, 'c0', 2),
  (201803, 'c1', 1),
  (201803, 'c2', 2),
  (201804, 'c0', null),
  (201804, 'c1', 2),
  (201804, 'c2', 5);
  
SELECT
  cnpj,
  anomes,
  x,
  sum(x) OVER w AS cumx
FROM (
  SELECT
    cnpj,
    anomes,
    x,
    count(x) OVER (PARTITION BY cnpj) AS countx
  FROM temp1
) t0
WHERE countx = 4  -- filtra empresas com historico completo
WINDOW w AS 
  (
    PARTITION BY cnpj
    ORDER BY anomes
    ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
  );