Prevent COUNT() Subquery using window functions
SELECT
T1.FIELD1,
T2.FIELD2,
...
NVL(T2.COMMENTS, 0) AS COMMENTS
FROM T1
LEFT OUTER JOIN 
(SELECT FOREIGN_KEY, COUNT (FIELD1) AS COMMENTS FROM OUTER_TABLE_NAME GROUP BY FOREIGN_KEY) T2
ON T2.FOREIGN_KEY = T1.PRIMARY_KEY
;