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user_knowledge_questions AS ukq
LEFT JOIN user_knowledge AS uk ON uk.id = ukq.user_knowledge_id
WHERE
uk.`status` = 0
ORDER BY
uk.end_time DESC
SELECT
ukq.*
FROM
user_knowledge_questions AS ukq
LEFT JOIN user_knowledge AS uk ON uk.id = ukq.user_knowledge_id
WHERE
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ORDER BY
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SELECT
ukq.*
FROM
(
SELECT
ukq.*
FROM
user_knowledge_questions AS ukq
LEFT JOIN user_knowledge AS uk ON uk.id = ukq.user_knowledge_id
WHERE
uk.`status` = 0
ORDER BY
uk.end_time DESC
) AS ukq
GROUP BY
ukq.questions_id