Mysql ORDER BY 和 LIMIT 慢查询

Question

我有以下查询，它在销售表中的 60,000 条记录上花费了大约 20 秒。我知道 ORDER BY 和 LIMIT 导致了这个问题，因为当 ORDER BY 被删除时，它会在 0.10 秒内返回。

我不确定如何优化这个查询，有什么想法吗？

解释输出在这里 https://gist.github.com/anonymous/1b92fa64261559de32da

SELECT sale.saleID as id, 
node.title as location, 
sale.saleTotal as total, 
sale.saleStatus as status, 
payment.paymentMethod, 
field_data_field_band_name.field_band_name_value as band, 
invoice.invoiceID, 
field_data_field_first_name.field_first_name_value as firstName, 
field_data_field_last_name.field_last_name_value as lastName, 
sale.created as date

FROM sale                  
LEFT JOIN payment
ON payment.saleID = sale.saleID
LEFT JOIN field_data_field_location
ON field_data_field_location.entity_id = sale.registerSessionID
LEFT JOIN node
ON node.nid = field_data_field_location.field_location_target_id    
LEFT JOIN invoice
ON invoice.saleID = sale.saleID                         
LEFT JOIN profile
ON profile.uid = sale.clientID                     
LEFT JOIN field_data_field_band_name
ON field_data_field_band_name.entity_id = profile.pid
LEFT JOIN field_data_field_first_name
ON field_data_field_first_name.entity_id = profile.pid
LEFT JOIN field_data_field_last_name
ON field_data_field_last_name.entity_id = profile.pid
ORDER BY sale.created DESC
LIMIT 0,50

Answer 1

可能，您无能为力。例如，当您衡量性能时，您是在查看返回第一个 记录的时间还是整个结果集？如果没有 order by，查询可以很快返回第一行，但您可能仍需要稍等片刻才能获取所有行。

假设比较有效，以下索引可能会有所帮助:sale(created, saleId, clientId, SaleTotal, SaleStatus。这是查询的覆盖索引，精心构造，以便可以按正确的顺序读取。如果这避免了最终排序，那么它应该会加快查询速度，即使是获取第一行也是如此。