Question

LEFT JOIN (SELECT xx_coinType AS yy_type, xx_sell AS sell_xx
           FROM xxs
           ORDER BY xx_id DESC) AS xxs
               ON xxs.yy_type = zz.zz_coin
LEFT JOIN (SELECT xx_coinType AS yy_type, xx_sell AS old_sell_xx
           FROM xxs
           WHERE xx_time < UNIX_TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 24 HOUR))
           ORDER BY xx_id DESC) AS old_xxs
               ON old_xxs.coin_type = zz.zz_coin

So I have 2 left joins in my query which select from same table but with a where on one. Since its the same table I select from the query is super slow. How can I fix this?

Answer 1

首先，不需要在派生表中使用order by子句其次，你的第一个派生表只是选择表中的所有记录，所以我不明白它的意义。

试试这个：

LEFT JOIN xxs
               ON xxs.yy_type = zz.zz_coin
LEFT JOIN (SELECT xx_coinType AS yy_type, xx_sell AS old_sell_xx
           FROM xxs
           WHERE xx_time < UNIX_TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 24 HOUR))
           ) AS old_xxs
               ON old_xxs.coin_type = zz.zz_coin

或者这个：

LEFT JOIN (SELECT xx_coinType AS yy_type, xx_sell AS sell_xx
           FROM xxs
           WHERE xx_time >= UNIX_TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 24 
           ) AS xxs
               ON xxs.yy_type = zz.zz_coin
LEFT JOIN (SELECT xx_coinType AS yy_type, xx_sell AS old_sell_xx
           FROM xxs
           WHERE xx_time < UNIX_TIMESTAMP(DATE_SUB(CURDATE(), INTERVAL 24 HOUR))
           ) AS old_xxs
               ON old_xxs.coin_type = zz.zz_coin

left join same table twice slow query

1 个答案: