mysql中关联变量条件修改、查询以及数据显示成一行的介绍

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