Question

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）

粗体表示主键。

我想写一个查询来查找供应每个部分的所有供应商。以下是我已经提出的两个问题：

-- get all parts for a given supplier
SELECT Parts.pid
FROM Suppliers
JOIN Catalog ON Catalog.sid = Suppliers.sid
JOIN Parts ON Parts.pid = Catalog.pid
WHERE Suppliers.sid = 4;

-- gets all parts that exist
SELECT Parts.pid
FROM Parts

在命令性的条件下，我想要做的是这样的事情：

Define result set
Foreach Supplier:
    If the list of parts produced by a supplier 
    is equal to the total list of parts, add this supplier to the result set
Return result set

如何将其转换为MySQL？

Answer 1

不确定它是如何转换为MySQL的，但也是如此：

select s.sname, PartCount from (
 select s.SID, s.sname, PartCount = sum(p.PID)
 inner join Catalog c on c.SID = s.SID
 inner join Parts p on p.PID = c.PID
 where s.SID = 4
 group by s.SID
) a
where PartCount = MAX(PartCount)

注意标记子查询“a”是一个任意名称，因为MSSQL由于某种原因需要在其子查询中使用名称。不知道它在MySQL中是如何工作的。

Answer 2

尝试（未经测试）：

SELECT s.*
FROM (
  SELECT sid, count(pid) as c
  FROM Catalog
  GROUP BY sid) q1
JOIN Suppliers s ON s.sid = q1.sid
WHERE q1.c = (SELECT COUNT(*) FROM Parts)

Answer 3

尝试：

SELECT Suppliers.sid
FROM Suppliers
INNER JOIN
(SELECT sid, COUNT(pid) as num
    FROM Catalog
    GROUP BY sid)as t1
ON Suppliers.sid = t1.sid
WHERE t1.num = 
    (SELECT COUNT(pid) FROM Parts)

Answer 4

使用：

SELECT s.*
  FROM SUPPLIER s
  JOIN (SELECT c.sid,
               COUNT(c.pid) AS num_parts
          FROM CATALOG c
      GROUP BY c.sid) x ON x.sid = s.sid
  JOIN (SELECT COUNT(*) AS total_parts
          FROM PARTS) y ON y.total_parts = x.num_parts

SQL：帮助嵌套查询

4 个答案: