pan_cras
2016-11-22 02:37
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sql 联表查询（两张表）

SELECT
    teacher_info.teacher_id,
    tearcher_name,
    teacher_number,
    tearcher_type,
    teacher_image,
    teacher_gender,
    teacher_birthday,
    identity_number,
    company,
    technical_title,
    technical_grade,
    major_type_id,
    major_id,
    courses_offer,
    phone,
    email,
    relative_material,
    LEVEL,
    country,
    province,
    city,
    region
FROM
    teacher_info,
    teacher_region_info
WHERE
    teacher_info.teacher_id = teacher_region_info.teacher_id

上面的语句会让teacher_region_info表中如果没有对应的teacher_id就使teacher_info的数据也不显示出来了，如何更改代码？

找到了答案：

SELECT
    teacher_info.teacher_id,
    tearcher_name,
    teacher_region_info.city
FROM
    teacher_info,
    teacher_region_info
WHERE
    teacher_info.teacher_id = teacher_region_info.teacher_id
UNION
    SELECT
        teacher_info.teacher_id,
        tearcher_name,
        teacher_region_info.city
    FROM
        teacher_info,
        teacher_region_info
    WHERE
        teacher_info.teacher_id != NULL
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7条回答 默认 最新

  • zhanjr 2016-11-22 02:53
    已采纳

    这时候需要用到外连接
    把from后面的改成
    from teacher_info left join teacher_region_info on teacher_info.teacher_id = teacher_region_info.teacher_id
    SQL的四种连接-左外连接、右外连接、内连接、全连接 建议楼主可以去学一下 很有用

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  • 圣-雄霸天下 2016-11-22 02:52
     select *
 from teacher_info
 left join teacher_region_info on teacher_region_info.teacher_id=teacher_info.teacher_id
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  • code_tai 2016-11-22 02:57

    现在不是已经实现了么？

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  • andy_2016 2016-11-22 03:10

    lz是不是没有把需求搞清楚？

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  • SELECT
    teacher_info.teacher_id,
    tearcher_name,
    teacher_number,
    tearcher_type,
    teacher_image,
    teacher_gender,
    teacher_birthday,
    identity_number,
    company,
    technical_title,
    technical_grade,
    major_type_id,
    major_id,
    courses_offer,
    phone,
    email,
    relative_material,
    LEVEL,
    country,
    province,
    city,
    region
    FROM
    teacher_info T1 LEFT JOIN teacher_region_info T2 ON T1.teacher_id = T2.teacher_id

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  • zhanjr 2016-11-22 03:23

    WHERE
    teacher_info.teacher_id = teacher_region_info.teacher_id(+)

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  • zhanjr 2016-11-22 03:27

    WHERE
    teacher_info.teacher_id = teacher_region_info.teacher_id(+)

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