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MySQL Left连接4个表，空行重复

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我坚持一个查询，我将以结果向后开始，以防这显而易见，然后提供更多细节 .

用户关注跟随供应商的赞助商，我正在尝试使用用户标识显示所有产品，其中存在用户标识的赞助供应商产品，没有用户标识为NULL .

Desired result (userid = 1):
productid |  supplierid  |  userid
    1            1            1
    2            1            1
    3            2           Null
    4            3            1
    5            2           Null
    6            3            1

Actual result (userid = 1):
productid |  supplierid  |  userid
    1            1            1
    1            1           Null
    2            1            1
    2            1           Null
    3            2           Null
    4            3            1
    4            3           Null
    5            2           Null
    6            3            1
    6            3           Null

我的查询：

SELECT product.productid, product.supplierid, usersponsor.userid FROM product 
INNER JOIN supplier ON product.supplierid = supplier.supplierid
LEFT JOIN sponsorsupplier ON sponsorsupplier.supplierid = product.supplierid
LEFT JOIN usersponsor ON usersponsor.sponsorid = sponsorsupplier.sponsorid and usersponsor.userid = 1

我有4张桌子

sponser
supplier
product
myuser

有了这两个链接表：

usersponsor
sponsorsupplier

示例表：

myuser:userid
  1
  2
  3
  4
  5

Sponsor:sponsorid
  1
  2
  3

Supplier:supplierid
  1
  2
  3

usersponsor
userid     |   sponsorid
  1        |       1     <- user 1 follows sponsor 1
  2        |       2
  2        |       3

sponsorsupplier
sponsorid  |   supplierid
  1        |       1     <- supplys product 1,2 (sponsor 1)
  1        |       3     <- supplys product 4,6 (sponsor 1)
  2        |       2 
  2        |       1
  3        |       3     


Product
productid  |  supplierid
  1        |      1       <-
  2        |      1       <-
  3        |      2
  4        |      3       <-
  5        |      2
  6        |      3       <-

谢谢你的帮助 .

mysql left-join

1 回答

  • 0

    您可以聚合子查询：

    SELECT
    p.productid
  , p.supplierid
  , ss.userid
FROM Product p
LEFT JOIN (
        SELECT
            ss.supplierid
          , MIN( us.userid ) userid
        FROM sponsorsupplier ss
        INNER JOIN usersponsor us ON ss.sponsorid = us.sponsorid
        WHERE us.userid = 1
        GROUP BY
            ss.supplierid
    ) ss ON p.supplierid = ss.supplierid
ORDER BY
    p.productid;
    回复于

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