我陷入了這樣一個境地：我有數百萬條記錄，並且需要不同的連接來實現相同的記錄。訂單條款也有一些棘手的部分。如果我不應用任何排序，我的查詢會執行快速結果。但在應用 order 子句時，需要花費太多時間才能得到結果。
如果沒有 Order 子句，則會導致 5-6 秒。
應用訂單條款時，結果為 40-45### 秒#
SELECT
forms_values.id,
CASE
WHEN forms_values.appointment_type = 2
AND user_patient_assinged_to_doctor.start_time IS NOT NULL
THEN
CASE
WHEN patient_responded_tags_logs.tag_set_at IS NOT NULL
THEN
CASE
WHEN UNIX_TIMESTAMP(
CONVERT_TZ(
patient_responded_tags_logs.tag_set_at,
"+00:00",
"-06:00"
)
) > UNIX_TIMESTAMP(
CONVERT_TZ(
STR_TO_DATE(
CONCAT(
user_patient_assinged_to_doctor.date,
" ",
user_patient_assinged_to_doctor.start_time
),
"%Y-%m-%d %h:%i %p"
),
"+00:00",
"-06:00"
)
)
THEN UNIX_TIMESTAMP(
CONVERT_TZ(
patient_responded_tags_logs.tag_set_at,
"+00:00",
"-06:00"
)
)
ELSE UNIX_TIMESTAMP(
CONVERT_TZ(
STR_TO_DATE(
CONCAT(
user_patient_assinged_to_doctor.date,
" ",
user_patient_assinged_to_doctor.start_time
),
"%Y-%m-%d %h:%i %p"
),
"+00:00",
"-06:00"
)
)
END
ELSE UNIX_TIMESTAMP(
CONVERT_TZ(
STR_TO_DATE(
CONCAT(
user_patient_assinged_to_doctor.date,
" ",
user_patient_assinged_to_doctor.start_time
),
"%Y-%m-%d %h:%i %p"
),
"+00:00",
"-06:00"
)
)
END
ELSE
CASE
WHEN patient_responded_tags_logs.tag_set_at IS NOT NULL
THEN
CASE
WHEN UNIX_TIMESTAMP(
CONVERT_TZ(
patient_responded_tags_logs.tag_set_at,
"+00:00",
"-06:00"
)
) > UNIX_TIMESTAMP(forms_values.created_at)
THEN UNIX_TIMESTAMP(
CONVERT_TZ(
patient_responded_tags_logs.tag_set_at,
"+00:00",
"-06:00"
)
)
ELSE UNIX_TIMESTAMP(forms_values.created_at)
END
ELSE UNIX_TIMESTAMP(forms_values.created_at)
END
END AS "consultation_date_time_ordering",
CASE
WHEN forms_values.appointment_type = 2
AND user_patient_assinged_to_doctor.start_time IS NOT NULL
THEN UNIX_TIMESTAMP(
CONVERT_TZ(
STR_TO_DATE(
CONCAT(
user_patient_assinged_to_doctor.date,
" ",
user_patient_assinged_to_doctor.start_time
),
"%Y-%m-%d %h:%i %p"
),
"+00:00",
"-06:00"
)
)
ELSE UNIX_TIMESTAMP(forms_values.created_at)
END AS "consultation_date_time" ,
CASE
WHEN forms_values.is_postpone = '1'
OR forms_values.is_completed = '8'
THEN
CASE
WHEN UNIX_TIMESTAMP(
CONVERT_TZ(
STR_TO_DATE(
CONCAT(UTC_DATE(), ' ', UTC_TIME()),
'%Y-%m-%d %h:%i:%s'
),
'+00:00',
'-06:00'
)
) < UNIX_TIMESTAMP(
my_list_postpone.postponed_date
)
THEN 0
ELSE 1
END
ELSE 1
END AS "postponed_consultation_ordering"
FROM
`forms_values`
LEFT JOIN `forms_values_completed_status_details`
ON `forms_values_completed_status_details`.`form_value_id` = `forms_values`.`id`
/*INNER JOIN `users`
ON `users`.`id` = `forms_values`.`patient_id`
LEFT JOIN `users` AS `doctors`
ON `doctors`.`id` = `forms_values`.`doctor_id`*/
LEFT JOIN `user_patient_assinged_to_doctor`
ON `user_patient_assinged_to_doctor`.`form_value_id` = `forms_values`.`id`
INNER JOIN `states_countries`
ON `forms_values`.`state` = `states_countries`.`id`
LEFT JOIN `user_payment_history`
ON `user_payment_history`.`form_value_id` = `forms_values`.`id`
LEFT JOIN `emailed_tags_logs`
ON `emailed_tags_logs`.`form_value_id` = `forms_values`.`id`
AND `emailed_tags_logs`.`id` =
(SELECT
emailed_tags_logs.id
FROM
emailed_tags_logs
WHERE emailed_tags_logs.form_value_id = forms_values.id
AND emailed_tags_logs.id =
(SELECT
emailed_tags_logs1.id AS emtid
FROM
emailed_tags_logs AS emailed_tags_logs1
WHERE emailed_tags_logs1.form_value_id = forms_values.id
ORDER BY emailed_tags_logs1.created_at DESC
LIMIT 1)
AND emailed_tags_logs.status IN (1, 3)
AND emailed_tags_logs.is_pt_responded = "0"
ORDER BY emailed_tags_logs.created_at DESC
LIMIT 1)
LEFT JOIN `my_list_assign_doctor`
ON `my_list_assign_doctor`.`form_value_id` = `forms_values`.`id`
AND `my_list_assign_doctor`.`id` =
(SELECT
my_list_assign_doctor.id
FROM
my_list_assign_doctor
WHERE my_list_assign_doctor.form_value_id = forms_values.id
AND my_list_assign_doctor.status IN (1, 2)
AND my_list_assign_doctor.prior_type = "others"
ORDER BY my_list_assign_doctor.created_at DESC
LIMIT 1)
LEFT JOIN `my_list_assign_doctor` AS `my_list_postpone`
ON `my_list_postpone`.`form_value_id` = `forms_values`.`id`
AND `forms_values`.`is_postpone` IN ('1', '2')
AND `my_list_postpone`.`id` =
(SELECT
my_list_assign_doctor.id
FROM
my_list_assign_doctor
WHERE my_list_assign_doctor.form_value_id = forms_values.id
AND my_list_assign_doctor.prior_type = "postpone"
ORDER BY my_list_assign_doctor.created_at DESC
LIMIT 1)
LEFT JOIN `users` AS `partner`
ON `user_payment_history`.`std_partner_id` = `partner`.`id`
LEFT JOIN `patient_responded_tags_logs`
ON `patient_responded_tags_logs`.`form_value_id` = `forms_values`.`id`
AND `patient_responded_tags_logs`.`status` = '1'
LEFT JOIN `user_subscriptions`
ON `user_subscriptions`.`user_payment_history_id` = `user_payment_history`.`id`
AND `user_payment_history`.`form_value_id` = `forms_values`.`id`
ORDER BY
postponed_consultation_ordering DESC,
`consultation_date_time` DESC
LIMIT 10 OFFSET 0
注意：所有聯結都很重要，出於某些考慮，欄位已從選擇查詢中刪除。 解釋摘要
問題出在 LIMIT 和 ORDER BY 的組合。
如果沒有 ORDER BY，一旦選擇了前十個隨機行，查詢就會停止。依照 order by 查詢必須收集所有可能的行，然後按順序對它們進行排序，然後只傳回前 10 行。
考慮到「postponed_consultation_datetime」是一個計算字段，確實沒有辦法讓它更快。