SQL：帮助进行嵌套查询

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：字符串，颜色：字符串）

目录（ >sid：整数，pid：整数，cost：实数）

粗体表示主键。

我想编写一个查询来查找提供每个零件的所有供应商。这是我已经有的两个查询：

-- 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

用命令式的术语来说，我想做的是这样的：

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

我怎样才能将其翻译成 MySQL？

Answer 1

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

Answer 2

不知道它如何转换为 MySQL，但大致如下：

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上使用名称。不知道它在 MySQL 中是如何工作的。

Answer 3

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 4

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)