加速MySQL加入以檢查重複項

Question

我正在使用以下查詢來返回具有相同姓氏和名字的所有重複記錄。訣竅是contact_id必須按降序排列。

查詢按預期返回聯繫人，但它只是如此慢！檢查大約30,000條記錄時需要大約6-8秒。

我有contact_firstName，contact_lastName，contact_client_id和contact_id在數據庫中索引所有。

任何想法，我可以做些什麼來加快這一點？感謝您的幫助:)

SELECT z.contact_id, z.contact_firstName, z.contact_lastName, RIGHT(z.contact_lastName,1) AS nameNum 
FROM (`contacts` x) 
JOIN `contacts` z ON `x`.`contact_firstName` = `z`.`contact_firstName` 
AND x.contact_lastName = z.contact_lastName 
AND x.contact_client_id = ".$ID." 
AND z.contact_client_id = ".$ID." 
WHERE `x`.`contact_id` < `z`.`contact_id` 
GROUP BY `z`.`contact_id` 

Answer 1

SELECT z.contact_id, z.contact_firstName, z.contact_lastName 
, RIGHT(z.contact_lastName,1) AS nameNum 
FROM `contacts` x 
JOIN `contacts` z ON (x.contact_client_id = z.contact_client_id) 
WHERE `x`.`contact_id` < `z`.`contact_id` 
And x.contact_client_id = '$id' 
GROUP BY `z`.`contact_id` 

確保您有一個指標：
- CONTACT_ID。
- contact_client_id

Answer 2

不作出任何承諾，但這裏是一個另類嘗試：

SELECT c.contact_id, c.contact_firstName, c.contact_lastName, RIGHT(c.contact_lastName,1) AS nameNum 
    FROM (SELECT contact_firstName, contact_lastName, MIN(contact_id) AS MinID 
       FROM contacts 
       WHERE contact_client_id = ".$ID." 
       GROUP BY contact_firstName, contact_lastName 
       HAVING COUNT(*) > 1) t 
     INNER JOIN contacts c 
      ON t.contact_firstName = c.contact_firstName 
       AND t.contact_lastName = c.contact_lastName 
       AND c.contact_client_id = ".$ID." 
       AND t.MinID <> c.contact_id