MariaDB 執行緩慢

不確定這是否可以在沒有 UNION 的情況下完成。我認為是 UNION 讓它變慢了。這兩個部分本身就相當快，但結合 UNION，此程式碼需要 > 5 秒才能完成。可以優化嗎？

SELECT rl.Updated, c.CultureName, 
"CollectionName" 
as CollectionName, k.KeyName , rl.Value , s.StatusName ,
rl.Comment , rl.Comment as ActionInfo, a.ActionName, u.UserName 
FROM ResourceLog rl 
INNER JOIN `Status` s ON rl.StatusId = s.StatusId 
INNER JOIN Culture c ON rl.CultureId = c.CultureId 
INNER JOIN `Key` k ON rl.KeyId = k.KeyId 
LEFT JOIN `Action` a ON rl.ActionId = a.ActionId 
LEFT JOIN `User` u ON rl.UserId = u.UserId 
UNION SELECT imp.Created as Updated, "Imported" as CultureName, 
"None" as CollectionName, "Imported" as KeyName, 
"Imported" as Value, "Imported" as StatusName, 
"Imported" as Comment, "ActionInfo" as ActionInfo, 
"Imported" as ActionName, UserId 
FROM Import imp 
ORDER BY Updated DESC, KeyName, CultureName limit 50

我懷疑組合查詢沒有做你認為它正在做的事情。

添加括號以明確第二個是ORDER BY屬於第二個SELECT還是屬於UNION. 同上LIMIT。

( SELECT ...
)
UNION
( SELECT ... 
    -- Do the ORDER BY and LIMIT belong here?
) 
-- Or here (for the UNION)?

如需進一步討論，請提供

EXPLAIN ...
SHOW CREATE TABLE ...
how big are the tables

引用自：https://dba.stackexchange.com/questions/229426