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_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,谢谢大家对脚本之家的支持。

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