雙左加入與MySQL的雙重計數？

select SQL_NO_CACHE a.id, 
     date_format(a.data_cron,'%d/%m/%Y às %H:%i:%s') as data_pt,a.msgal, 
     a.status, 
     b.nome, 
     c.msg, 
     if((select count(*) from moips_temps where envio_id=a.id group by envio_id) > 0,1,0) as senvio, 
     if((select count(*) from moips_temps2 where envio_id=a.id group by envio_id) > 0,1,0) as senvio2 
    from moips_envios a, 
     moips_listas b, 
     moips_msgs c 
where a.lista_id = b.id 
    and a.msg_id = c.id 
    and a.moips_id = 44 
order by a.id desc

時間：0.0146雙左加入與MySQL的雙重計數？

select SQL_NO_CACHE a.id,date_format(a.data_cron,'%d/%m/%Y às %H:%i:%s') as data_pt, a.msgal, a.status, b.nome, c.msg, 
    if(count(d.envio_id) > 0,1,0) as senvio, 
    if(count(e.envio_id) > 0,1,0) as senvio2 
from moips_envios a 
left join moips_temps d 
    on a.id=d.envio_id 
left join moips_temps2 e 
    on a.id=e.envio_id, moips_listas b, moips_msgs c 
where a.lista_id=b.id 
    and a.msg_id=c.id 
    and a.moips_id=25 
group by a.id 
order by a.id desc

時間：0.1107

爲什麼與子查詢數更快速？

來源

2012-04-15 Rafael Osvaldo

PLS格式的代碼/查詢 - 比較難讀，我們要幫助的可能性就越小。 – 2012-04-15 03:32:26

好吧，我會做的秒 – 2012-04-15 03:33:15

沒有1可以解釋它對我？ – 2012-04-15 04:06:01

一個非常簡單的改進，非標，僅在MySQL中，正在發生變化：

GROUP BY a.id 
ORDER BY a.id DESC

到：

GROUP BY a.id DESC

來源

2012-04-15 08:40:43

雙左加入與MySQL的雙重計數？

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