需要這個查詢中的「前五名」id

Question

我之前有人幫助我，並且已經接近了，我需要從這個查詢中得到前五名「id's」。發生了什麼？ ？ID而不是前五名的任何人都知道如何解決這個下面是該查詢：

(
SELECT id, 
    firstName, 
    lastName, 
    SUM(fileSize) AS TotalBytes, 
    SUM(fileSize)/COUNT(*) AS Average 
FROM roster_cs368 AS a 
JOIN htmp_cs368 AS b USING (id) 
) UNION (
SELECT id, 
    firstName, 
    lastName, 
    SUM(fileSize) AS TotalBytes, 
    SUM(fileSize)/COUNT(*) AS Average 
FROM roster_cs368 AS a 
JOIN atmp_cs368 AS b USING (id) 
) 
ORDER BY TotalBytes DESC 
LIMIT 5 

謝謝這也是一個更大的計劃的一部分，因此Java標記

這裏是。模式：

mysql> select * from roster_cs368 
-> ; 
+--------+-----------+-----------+ 
| id  | firstName | lastName | 
+--------+-----------+-----------+ 
| apn7cf | Allen  | Newton | 
| atggg3 | andrew | goebel | 

哪裏是主鍵，

mysql> select * from htmp_cs368; 
+------------+----------+------------+----------+----------+-------+------+-------+----------------------+ 
| filePerms | numLinks | id   | idGroup | fileSize | month | day | time | fileName    | 
+------------+----------+------------+----------+----------+-------+------+-------+----------------------+ 
| drwx------ |  2 | schulte | faculty |  289 | Nov | 7 | 2011 | Java     | 
| -rw-r--r-- |  1 | schulte | faculty |  136 | Apr | 29 | 2012 | LD     | 
| drwxr-xr-x |  3 | schulte | faculty |  177 | Mar | 20 | 2012 | Upgrade    | 

這裏沒有主鍵，

mysql> select * from atmp_cs368; 
+------------+----------+--------------+----------+----------+-------+------+-------+-----------------------------+ 
| filePerms | numLinks | id   | idGroup | fileSize | month | day | time | fileName     | 
+------------+----------+--------------+----------+----------+-------+------+-------+-----------------------------+ 
| drwxr-xr-x |  2 | remierm  | 203  |  245 | Sep | 17 | 14:40 | 148360_sun_studio_12  | 
| drwx---rwx |  31 | antognolij | sasl  |  2315 | Oct | 24 | 12:28 | 275       | 
| -rwx------ |  1 | kyzvdb  | student |  36 | Sep | 19 | 13:05 | 275hh      | 

這裏沒有主鍵。

什麼我的查詢是：

produce a list of the five members of roster_cs368, 
    and their ids who use the most space (number of bytes) 
    in htmp_cs368 and atmp_cs368 in descending order-- 
    greediest first. display total number of bytes and 
    average size of file 

Answer 1

你可以這樣說：

SELECT * FROM(
(
SELECT id, 
    firstName, 
    lastName, 
    SUM(fileSize) AS TotalBytes, 
    SUM(fileSize)/COUNT(*) AS Average 
FROM roster_cs368 AS a 
JOIN htmp_cs368 AS b USING (id) 
) UNION (
SELECT id, 
    firstName, 
    lastName, 
    SUM(fileSize) AS TotalBytes, 
    SUM(fileSize)/COUNT(*) AS Average 
FROM roster_cs368 AS a 
JOIN atmp_cs368 AS b USING (id) 
) 
) as somealias ORDER BY TotalBytes DESC 
LIMIT 5