现在有 2 个表,要在第一个表结果集的基础上在查询第二表的数据, - V2EX
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cnmllll
V2EX    MySQL

现在有 2 个表,要在第一个表结果集的基础上在查询第二表的数据,

  •  
  •   cnmllll Nov 13, 2018 3475 views
    This topic created in 2721 days ago, the information mentioned may be changed or developed.

    例子: 表 1 字段:a b c d

    表 2 字段:e f

    表一的字段 c 可以在表 2 字段 e 找到,我现在想一条 sql 语句查出 a b c d f 这 5 个字段 sql 小白,求指点~

    8 replies    2018-11-13 17:59:41 +08:00
    LucasLee92
        1
    LucasLee92  
       Nov 13, 2018
    left join
    TomVista
        2
    TomVista  
       Nov 13, 2018
    自行百度 mysql join
    cnmllll
        3
    cnmllll  
    OP
       Nov 13, 2018
    @LucasLee92 xiexie jie jue le SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a INNER JOIN tcount_tbl b ON a.runoob_author = b.runoob_author
    TommyLemon
        4
    TommyLemon  
       Nov 13, 2018
    ```sql
    SELECT t1.a, t1.b, t1.c, t1.d, t2.f FROM t1 INNER JOIN t2 ON t1.c = t2.e
    ```
    看你的需求,INNER JOIN 可能要改成 LEFT JOIN 等。

    还可以用全自动化的 ORM 库 APIJSON,不用写代码,直接让前端传
    {
    "[]": {
    "join": "&/T2/e@",
    "T1": {},
    "T2": {
    "e@": "/T1/c"
    }
    }
    }
    后端就自动生成的和上面几乎一样的 SQL。
    可以用这个测试:
    {
    "[]": {
    "join": "&/User/id@",
    "Comment": {},
    "User": {
    "id@": "/Comment/userId"
    }
    }
    }
    复制到 APIJSONAuto 自动化接口管理平台,点击 [发送请求]
    apijson。org
    fiypig
        5
    fiypig  
       Nov 13, 2018
    select * form 1,2 where 1.c = 2.e
    TommyLemon
        6
    TommyLemon  
       Nov 13, 2018
    @TommyLemon
    后端接口和文档自动化,前端(客户端) 定制返回 JSON 的数据和结构!
    GitHub 右上角点 Star 支持下吧 ^_^
    github.com/TommyLemon/APIJSON/
    TommyLemon
        7
    TommyLemon  
       Nov 13, 2018
    @fiypig MySQL 貌似不支持这种隐式 JOIN,PostgreSQL 倒是可以。问题要求 MySQL
    flowfire
        8
    flowfire  
       Nov 13, 2018 via iPhone
    子查询可能比 join 要快。。。
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