mysql - SQL : Cartesian product + Join + Flatten

Question

在 MYSQL 5.6 下，我有以下 2 个表:

CREATE TABLE User
(
    id        INTEGER,
    login     VARCHAR(32),
    isservice BOOLEAN
);

CREATE TABLE Certificate
(
    userid        INTEGER,
    serviceid     INTEGER,
    certificate   VARCHAR(32)
);

具有以下数据:

用户:

id  |  login   |  isservice
---------------------------
1   | john     | false
2   | bob      | false
3   | serviceA | true
4   | serviceB | true

证书:(示例数据，证书列中的真实数据未知)

userid | serviceid | Certificale
---------------------------
1      | 3         | Alpha
1      | 4         | Bravo

我创建了以下 SQLFiddle:http://sqlfiddle.com/#!9/719a8/2

我正在搜索会给我以下内容的请求(不是存储过程):

id | login | certif_serviceA | certif_serviceB
-----------------------------------------------
1  | john  | Alpha           | Bravo
2  | bob   | NULL            | NULL

到目前为止，我已经尝试将我的请求基于:

SELECT  user.id, user.login,
        service.login as serviceName
FROM User, User as service WHERE service.isservice=1 AND user.isservice=0

但我被困在那里:s

Answer 1

正如我已经评论过的，您绝对应该重新设计您的数据库。

您要的是 pivot table，使用 mysql 实现起来并不容易。你可以阅读here

但我为您提供了这种方法:

http://sqlfiddle.com/#!9/4dc0b2/1

SELECT  user.id, user.login,
    GROUP_CONCAT(Services.login) as ServicesName,
    GROUP_CONCAT(certificate.certificate) as Certificates
FROM User
LEFT JOIN Certificate
ON Certificate.userid = User.id
LEFT JOIN User Services
ON Certificate.serviceid = Services.id
WHERE NOT User.isservice
GROUP BY User.id

或

SELECT  user.id, user.login,
    GROUP_CONCAT(CONCAT(Services.login,':',certificate.certificate)) as ServicesName
FROM User
LEFT JOIN Certificate
ON Certificate.userid = User.id
LEFT JOIN User Services
ON Certificate.serviceid = Services.id
WHERE NOT User.isservice
GROUP BY User.id

对于当前情况，您可能可以接受。

更新

SELECT  user.id, user.login,
    GROUP_CONCAT(Services.login) as ServicesName,
    GROUP_CONCAT(certificate.certificate) as Certificates
FROM User
LEFT JOIN User Services
ON Services.isservice
LEFT JOIN Certificate
ON Certificate.userid = User.id
  AND Certificate.serviceid = Services.id
WHERE NOT User.isservice
GROUP BY User.id

http://sqlfiddle.com/#!9/1c062/4