mysql中的一些稍微复杂用法实例代码

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)。 &nbsp 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_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 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 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

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。