如何在没有子查询的情况下为以下查询编写sql

Question

SELECT C.pid
FROM Catalog C, Suppliers S
WHERE S.sname = ‘Yosemite Sham’ AND C.sid = S.sid
AND C.cost ≥ ALL (Select C2.cost
FROM Catalog C2, Suppliers S2
 WHERE S2.sname = ‘Yosemite Sham’ AND C2.sid = S2.sid)

Answer 1

First, learn to use proper, explicit JOIN syntax.

Then, if you assume that the maximum cost occurs only once, you can do:

SELECT C.pid
FROM Catalog C JOIN
     Suppliers S
     ON C.sid = S.sid
WHERE S.sname = 'Yosemite Sham'
ORDER BY  c.Cost DESC
FETCH FIRST 1 ROW ONLY ;

Note that the last clause is ANSI standard SQL. Some databases use other methods for the same functionality.

Without this assumption, basically all reasonable methods use a subquery. Here is one that doesn't:

SELECT C.pid
FROM Catalog C JOIN
     Suppliers S
     ON C.sid = S.sid LEFT JOIN
     Catalog C2
     ON C2.sid = C.sid AND
        C2.Cost > C.Cost
WHERE S.sname = 'Yosemite Sham' AND c2.Cost IS NULL
ORDER BY c.Cost DESC;

Note: This assumes that sid is 1-1 with sname . That is a convenience (which is likely to be true) and helps avoid an extra join to Suppliers .