我有一個由兩個快速查詢組成的UNION查詢。緩慢UNION查詢 - MySQL
(SELECT DISTINCT (SELECT strStatus FROM User_User_XR uuxr WHERE
(uuxr.intUserId1 = '1' AND uuxr.intUserId2 = u.intUserId)) AS strFriendStatus1,
uuxro.strStatus AS strFriendStatus2, uuxr.intUserId2 AS intUserId, u.strUserName ,
u.strGender, IF(u.dtmBirth != '0000-00-00', FLOOR(DATEDIFF(CURDATE(),
u.dtmBirth)/365.25) , '?') AS intAge, u.strCountry AS strCountryCode,
c.strCountry AS strCountry, u.strAvatar, u.fltPoints,
IF(o.intUserId IS NULL, 'offline', 'online') AS strOnline,
IF (u.strAvatar != '', CONCAT('avatars/60/', u.strAvatar),
CONCAT('images/avatar_', u.strGender, '_small.png')) as strAvatar,
IF (u.strAvatar != '', CONCAT('avatars/150/', u.strAvatar),
CONCAT('images/avatar_', u.strGender, '.png')) as strLargeAvatar,
u.dtmLastLogin, u.dtmRegistered FROM User_User_XR uuxr,
User u LEFT JOIN User_User_XR uuxro ON uuxro.intUserId2 = '1'
AND uuxro.intUserId1 = u.intUserId
LEFT JOIN Online o ON o.intUserId = u.intUserId
LEFT JOIN Country c ON c.strCountryCode = u.strCountry
WHERE u.intUserId = uuxr.intUserId2 AND (uuxr.strStatus = 'confirmed')
AND uuxr.intUserId1='1')
UNION
(SELECT DISTINCT (SELECT strStatus FROM User_User_XR uuxr
WHERE (uuxr.intUserId1 = '1' AND uuxr.intUserId2 = u.intUserId)) AS strFriendStatus1,
uuxro.strStatus AS strFriendStatus2, uuxr.intUserId1 AS intUserId, u.strUserName ,
u.strGender, IF(u.dtmBirth != '0000-00-00', FLOOR(DATEDIFF(CURDATE(),
u.dtmBirth)/365.25) , '?') AS intAge,
u.strCountry AS strCountryCode, c.strCountry AS strCountry, u.strAvatar, u.fltPoints,
IF(o.intUserId IS NULL, 'offline', 'online') AS strOnline,
IF (u.strAvatar != '', CONCAT('avatars/60/', u.strAvatar),
CONCAT('images/avatar_', u.strGender, '_small.png')) as strAvatar,
IF (u.strAvatar != '', CONCAT('avatars/150/', u.strAvatar),
CONCAT('images/avatar_', u.strGender, '.png')) as strLargeAvatar,
u.dtmLastLogin, u.dtmRegistered FROM User_User_XR uuxr, User u
LEFT JOIN User_User_XR uuxro ON uuxro.intUserId2 = '1'
AND uuxro.intUserId1 = u.intUserId
LEFT JOIN Online o ON o.intUserId = u.intUserId
LEFT JOIN Country c ON c.strCountryCode = u.strCountry
WHERE u.intUserId = uuxr.intUserId1 AND (uuxr.strStatus = 'confirmed')
AND uuxr.intUserId2='1')
查詢首先在0.0047s 二運行運行在0.0043s
然而,與工會,他們跑0.27s ......這是爲什麼?在UNION之後沒有Order By,爲什麼MySQL不會簡單地使用這兩個快速查詢並將它們連接起來?
聯盟所有減少到0.17s ..它做了一些事情,但它仍然太慢... :(謝謝答案:) – Armin 2010-08-19 17:54:47