條件語句中的MySQL子查詢

Question

我有一個小的問題，作爲條件的子查詢。

這是我試圖找出代碼：

SELECT `page` 
    FROM `mdl_tool_devcourse` 
    WHERE `page` IN 
      (SELECT `objectid` 
      FROM `mdl_logstore_standard_log` 
      WHERE `action` = 'viewed' AND `objecttable` = 'wiki_pages' AND `userid` = 2) 

      AND `ref` IN 

      (SELECT `objectid` 
      FROM `mdl_logstore_standard_log` 
      WHERE `action` = 'viewed' AND `objecttable` = 'wiki_pages' AND `userid` = 2) 

所以在我的WHERE語句我想都page和ref是從我的子查詢的結果中。爲了達到這個目的，我找不到其他任何方式，而不是兩次運行子查詢。是否有另外一個選項讓子查詢只執行一次？

Answer 1

子查詢超慢。嘗試運行該查詢：

SELECT 
    `mdl_tool_devcourse`.`page` 
FROM `mdl_tool_devcourse` 
INNER JOIN `mdl_logstore_standard_log` ON `mdl_logstore_standard_log`.`action` = 'viewed' 
    AND `mdl_logstore_standard_log`.`objecttable` = 'wiki_pages' 
    AND `mdl_logstore_standard_log`.`userid` = 2 
    AND `mdl_tool_devcourse`.`page` = `mdl_logstore_standard_log`.`objectid` 
    AND `mdl_tool_devcourse`.`page` = `mdl_logstore_standard_log`.`ref`