本篇文章給大家帶來的內容是關于mysql中關聯變量條件修改、查詢以及數據顯示成一行的介紹（附代碼），有一定的參考價值，有需要的朋友可以參考一下，希望對你有所幫助。
一對多數據顯示成一行
GROUP_CONCAT(expr)
1、涉及的表關系:teacher表、teacher_subject_rel表(教師所能教的學科表)、subject表
2、業務場景: 需要拉取所有教師的編號(teacher_no)、學科名(subject_name)。?  教師表(teacher)和學科(teacher_subject_rel)是一對多關系, ?往往查詢出現的是同一教師多條 ? ?數據。我們希望得到每個教師一條數據 學科拼接成一條
1、基本語法
group_concat( [DISTINCT] ?要連接的字段 ? [Order BY 排序字段 ASC/DESC] ? [Separator ‘分隔符’] )
2、例子
SELECT t.teacher_id as '教師id', t.teacher_no '教師編號', ( SELECT GROUP_CONCAT(s.subject_name) FROM teacher_subject_rel tsr LEFT JOIN `subject` s ON tsr.subject_id = s.subject_id WHERE t.teacher_id = tsr.teacher_id ) AS '學科' FROM teacher t
子查詢、查詢臨時表、EXISTS
例子
SELECT * FROM ( SELECT o.id, o.student_intention_id, s. NAME, s.area_id, a.area_name, s.exam_year, o. STATUS, CASE o. STATUS WHEN '1' THEN '待提交' WHEN '2' THEN '待指派' WHEN '3' THEN '已完成' WHEN '4' THEN '處理中' END statusName, CASE o.emergency_degree WHEN '1' THEN '正常' WHEN '2' THEN '緊急' WHEN '3' THEN '非常緊急' END emergencyDegreeName, o.emergency_degree, o.update_time, ( SELECT first_lesson_time FROM jx_strategy WHERE jx_lesson_plan_order_id = o.id AND STATUS IN (2, 7) AND first_lesson_time > now() ORDER BY first_lesson_time ASC LIMIT 1 ) AS first_time, ( SELECT deal_user_id FROM jx_strategy WHERE jx_lesson_plan_order_id = o.id AND STATUS <> 7 AND deal_user_id <> 0 ORDER BY id DESC LIMIT 1 ) AS deal_user_id FROM jx_lesson_plan_order o LEFT JOIN student s ON s.student_intention_id = o.student_intention_id LEFT JOIN area a ON s.area_id = a.id WHERE o. STATUS <> 1 AND s.phone = '18501665888' AND o.emergency_degree = 1 AND o. STATUS = 2 AND s.exam_year = '2015' AND o.update_time >= '2018-08-14 20:28:55' AND o.update_time <= '2018-08-14 20:28:55' ) AS a WHERE 1 = 1 AND a.deal_user_id = 145316 AND a.first_time >= '2018-08-17 00:00:00' AND a.first_time <= '2018-08-30 00:00:00' AND EXISTS ( SELECT * FROM jx_strategy js WHERE js.jx_lesson_plan_order_id = a.id AND js. STATUS IN (2, 7) AND js.subject_id IN (2, 3) ) ORDER BY a.update_time DESC LIMIT 0, 10
update 關聯變量條件修改
1、涉及的表關系: ?user_info表中的 id_number(身份證號) ? teacher表中的birth字段、 關聯關系usrer_id = teacher_id
2、業務場景：獲取用戶身份證上的出生日期將出生日期更新在birth字段
UPDATE teacher t INNER JOIN ( SELECT t.teacher_id, t.birth, u.id_number, CONCAT(SUBSTRING(u.id_number, 7, 4), '-', SUBSTRING(u.id_number, 11, 2), '-', SUBSTRING(u.id_number, 13, 2)) as birth1, u.reg_date, t.exit_time from teacher t INNER JOIN user_info u ON u.user_id = t.teacher_id ) info on info.teacher_id = t.teacher_id SET t.birth = info.birth1 WHERE info.reg_date > '2018-08-20 00:00:00' and info.id_number is not NULL and (info.birth is NULL or t.birth = '') and t.is_train = 1
? ? ? ??
? 版權聲明
文章版權歸作者所有，未經允許請勿轉載。
THE END
