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)。 &nbsp 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

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