1つのクエリで異なる条件でカウントすることは可能ですか？

これを実現するには、ピボットクエリが必要です：

SELECT SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 1  THEN 1 ELSE 0 END) AS Jan,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 2  THEN 1 ELSE 0 END) AS Feb,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 3  THEN 1 ELSE 0 END) AS Mar,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 4  THEN 1 ELSE 0 END) AS Apr,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 5  THEN 1 ELSE 0 END) AS May,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 6  THEN 1 ELSE 0 END) AS Jun,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 7  THEN 1 ELSE 0 END) AS Jul,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 8  THEN 1 ELSE 0 END) AS Aug,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 9  THEN 1 ELSE 0 END) AS Sep,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 10 THEN 1 ELSE 0 END) AS Oct,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 11 THEN 1 ELSE 0 END) AS Nov,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 12 THEN 1 ELSE 0 END) AS Dec
FROM Shipments
WHERE EXTRACT(YEAR FROM dateshipped)::int=2016