Question

我正在使用MySQL。这是我的架构：

供应商（ sid：整数，sname：字符串，地址字符串）

零件（ pid：整数，pname：string，color：string）

目录（ sid：整数，pid：整数，成本：真实）

（主键以粗体显示）

我正在尝试编写一个查询，选择提供相同部分的sid对：

-- Find pairs of SIDs that both supply the same part
SELECT s1.sid, s2.sid
FROM Suppliers AS s1, Suppliers AS s2
JOIN Catalog ON s1.sid = Catalog.sid OR s2.sid = Catalog.sid;

MySQL给了我这个错误：

ERROR 1054（42S22）：未知列 's1.sid'在'on clause'

我做错了什么？

Answer 1

您正在混合ANSI-89和ANSI-92 JOIN语法 - 您只能使用一个或另一个。 ANSI-92：

   SELECT s1.sid, s2.sid
     FROM CATALOG c
LEFT JOIN SUPPLIERS s1 ON s1.sid = c.sid
LEFT JOIN SUPPLIERS s2 ON s2.sid = c.sid

如果要查看与两个供应商相关联的类别，请忽略LEFT关键字。

ANSI-89语法包含在FROM子句中声明的所有表，连接在WHERE子句中。

使用ANSI-92 - see this question for details。

Answer 2

您正在加入s2和目录。 s1在该子句中不存在。

Answer 3

我不明白错误信息，但是：

在这种情况下我会避免使用join。试试这个

SELECT s1.sid, s2.sid
FROM suppliers s1,
     suppliers s2,
     catalog   c1,
     catalog   c2
WHERE c1.pid = c2.pid
AND   s1.sid = c1.sid
AND   s2.sid = c2.sid
AND   s1.sid < s2.sid

虽然你所要求的只是sids，但它可以更简单：

SELECT c1.sid, c2.sid
FROM catalog   c1,
     catalog   c2
WHERE c1.pid = c2.pid
AND   c1.sid < c2.sid

Answer 4

如果您将使用显式连接，我认为您需要显式连接所有表。

e.g。

-- Find pairs of SIDs that both supply the same part
SELECT 
  s1.sid, 
  s2.sid
FROM 
  Catalog 

    LEFT OUTER JOIN 
  Suppliers AS s1,
    ON Catalog.sid = s1.sid

    LEFT OUTER JOIN
  Suppliers AS s2
    ON Catalog.sid = s2.sid

Answer 5

您需要自己加入目录

SELECT 
    pid, 
    c1.sid, 
    c2.sid
FROM Catalog c1
JOIN Catalog c2 ON c1.pid = c2.pid AND c1.sid < c2.sid

＆LT;条件是避免成对（A提供与B相同的X，因此B提供与A相同的X）

Answer 6

找到两个或更多供应商的零件：

select part_id
from catalog 
group by part_id
having count(part_id) >= 2

找到这些零件的供应商，更具前瞻性，可以展示两个或更多供应商：

select c.part_id, s.supplier_name 
from catalog c
join supplier s
where c.part_id in (
    select part_id
    from catalog 
    group by part_id
    having count(part_id) >= 2)
order by c.part_id, s.supplier_name

但如果你想要的零件只有两个供应商：

select c.part_id, group_concat(s.supplier_name) as suppliers 
from catalog c
join supplier s using(supplier_id)
where part_id in (
    select part_id
    from catalog 
    group by part_id
    having count(part_id) = 2)
group by c.part_id

如果你只想让这两个供应商在两栏中展示......我也在考虑......： - ）

[UPDATE]

我的想法：

select c.part_id, c.min(c.supplier_id) as first, c.max(c.supplier_id) as second 
from catalog c
join supplier s
where c.part_id in (
    select part_id
    from catalog 
    group by part_id
    having count(part_id) = 2)
group by c.part_id
order by c.part_id

获取供应商名称：

select x.part_id, a.supplier_name, b.supplier_name from
(
    select c.part_id, c.min(c.supplier_id) as first, c.max(c.supplier_id) as second 
    from catalog c
    join supplier s
    where c.part_id in (
        select part_id
        from catalog 
        group by part_id
        having count(part_id) = 2)
    group by c.part_id
    order by c.part_id
 ) as x
 join supplier a on x.first = a.sid
 join supplier b on x.second = b.sid

SQL：在FROM子句中有两次表

6 个答案: