mysql中的一些稍微复杂用法实例代码

数据库  /  管理员 发布于 6年前   131

前言

mysql的语法相信对大家来说都不是难事，但是本文主要给分享了一些mysql复杂用法的相关内容，通过这篇文章相信大家会对mysql更深的了解一些，下面话不多说了，来一起看看详细的介绍吧

一对多数据显示成一行

GROUP_CONCAT(expr)

1、涉及的表关系:teacher表、teacher_subject_rel表(教师所能教的学科表)、subject表
2、业务场景: 需要拉取所有教师的编号(teacher_no)、学科名(subject_name)。   教师表(teacher)和学科(teacher_subject_rel)是一对多关系, 往往查询出现的是同一教师多条 数据。我们希望得到每个教师一条数据 学科拼接成一条

1、基本语法

group_concat( [DISTINCT] 要连接的字段 [Order BY 排序字段 ASC/DESC] [Separator '分隔符'] )

2、例子

SELECT t.teacher_id as '教师id', t.teacher_no '教师编号', ( 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 '学科'FROM teacher t

子查询、查询临时表、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   '处理中'  END statusName,  CASE o.emergency_degree WHEN '1' THEN  '正常' WHEN '2' THEN  '紧急' WHEN '3' THEN  '非常紧急' 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_idFROM jx_lesson_plan_order oLEFT JOIN student s ON s.student_intention_id = o.student_intention_idLEFT JOIN area a ON s.area_id = a.idWHERE o. STATUS <> 1AND s.phone = '18501665888'AND o.emergency_degree = 1AND o. STATUS = 2AND 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 aWHERE 1 = 1AND a.deal_user_id = 145316AND 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 DESCLIMIT 0, 10

update 关联变量条件修改

1、涉及的表关系: user_info表中的 id_number(身份证号) teacher表中的birth字段、 关联关系usrer_id = teacher_id
2、业务场景：获取用户身份证上的出生日期将出生日期更新在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 tINNER JOIN user_info u ON u.user_id = t.teacher_id) info on info.teacher_id = t.teacher_idSET t.birth = info.birth1WHERE 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

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对的支持。