Question

我有两个相同的SQL查询，我想合并结果。第一个是：

SELECT USER.USER_ID, NAME, SURNAME, EMAIL, STATUS, PHOTO 
FROM FRIENDLIST, USER, USER_PROFILE 
WHERE FRIENDLIST.USER_ID=". $userID ." 
  AND APPROVED='YES' 
  AND USER.USER_ID=FRIENDLIST.USER_ID 
  AND USER.USER_ID=USER_PROFILE.USER_ID

第二个是：

SELECT USER.USER_ID, NAME, SURNAME, EMAIL, STATUS, PHOTO 
FROM FRIENDLIST, USER, USER_PROFILE 
WHERE FRIENDLIST.FRIEND_ID=". $userID ."
  AND APPROVED='YES' 
  AND USER.USER_ID=FRIENDLIST.USER_ID 
  AND USER.USER_ID=USER_PROFILE.USER_ID

我尝试使用union但是我获得了一个空结果而不是$ userID = 2的2行。

SELECT USER.USER_ID, NAME, SURNAME, EMAIL, STATUS, PHOTO
FROM FRIENDLIST, USER, USER_PROFILE 
WHERE FRIENDLIST.USER_ID=". $userID ." 
  AND APPROVED='YES' 
  AND USER.USER_ID=FRIENDLIST.USER_ID 
  AND USER.USER_ID=USER_PROFILE.USER_ID 
UNION
SELECT USER.USER_ID, NAME, SURNAME, EMAIL, STATUS, PHOTO 
FROM FRIENDLIST, USER, USER_PROFILE
WHERE FRIENDLIST.FRIEND_ID=". $userID ." 
  AND APPROVED='YES' 
  AND USER.USER_ID=FRIENDLIST.USER_ID 
  AND USER.USER_ID=USER_PROFILE.USER_ID

任何想法??

Answer 1

我会像这样把它们结合起来：

SELECT USER.USER_ID, NAME, SURNAME, EMAIL, STATUS, PHOTO 
FROM FRIENDLIST, USER, USER_PROFILE 
WHERE (FRIENDLIST.USER_ID=". $userID ." or FRIENDLIST.FRIEND_ID=". $userID .")
  AND APPROVED='YES' 
  AND USER.USER_ID=FRIENDLIST.USER_ID 
  AND USER.USER_ID=USER_PROFILE.USER_ID

嗯，严格来说并非如此。我会使用适当的连接语法并为表使用短别名：

SELECT u.USER_ID, NAME, SURNAME, EMAIL, STATUS, PHOTO 
FROM FRIENDLIST f join
     USER u
     on u.USER_ID = f.USER_ID  join
     USER_PROFILE up
     on u.USER_ID = up.USER_ID
WHERE (f.USER_ID=". $userID ." or f.FRIEND_ID=". $userID .") and
      APPROVED='YES'

union是做同样事情的另一种效率较低的方法。如果结果集为空，那是因为没有人符合条件。

合并两个相同的选择查询

1 个答案: