1.嵌套查询优化
优化前
SELECT
q.id,
q.title,
q.question,
q.person_name,
q.department_name,
r.response,
r.create_time response_time
FROM
tb_ent_question q
LEFT JOIN tb_ent_response r ON q.id = r.question_id
WHERE
r.create_time = (
SELECT
MAX(create_time)
FROM
tb_ent_response r1
WHERE
r1.question_id = q.id
)
OR r.create_time IS NULL
ORDER BY
q.create_time DESC优化后
SELECT
q.id,
q.title,
q.question,
q.person_name,
q.department_name,
r.response,
r.create_time response_time
FROM
tb_ent_question q
LEFT JOIN tb_ent_response r ON q.id = r.question_id,
(
SELECT
r1.id,
r1.question_id,
max(r1.create_time) AS create_time
FROM
tb_ent_response r1
GROUP BY
id
) a
WHERE
(
a.id = r.id
OR (r.create_time IS NULL)
)
GROUP BY
q.id
ORDER BY
q.create_time DESC
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