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、
select * from Article atk
where
(is_doc=1 and not exists (select 1 from Comment cmt where cmt.atk_id = atk.id))
or is_doc=0
SELECT T1.*
FROM ARTICLE T1
WHERE T1.IS_DOC = 1
AND NOT EXISTS (SELECT 1 FROM COMMENT T2 WHERE T1.ID = T2.ATK_ID)
UNION ALL
SELECT T1.*
FROM ARTICLE T1, COMMENT T2
WHERE T1.IS_DOC = 0
AND T1.ID = T2.ATK_ID;