mysql如何在后端工作

Question

鉴于以下两个查询，如果存在任何差异，哪一个会更快（理论上）。

SELECT `ViewCounterView`.`id`, `ViewCounterView`.`referer`, 
(COUNT(`ViewCounterView`.`id`)) AS `ViewCounterView__referer_count`, 
(LOCATE("http", `ViewCounterView`.`referer`) >= 1) AS `ViewCounterView__external` 
FROM `dogmatic69`.`view_counter_views` AS `ViewCounterView` 
WHERE `ViewCounterView`.`referer` IS NOT NULL 
GROUP BY `ViewCounterView`.`referer` 
ORDER BY (LOCATE("http", `ViewCounterView`.`referer`) >= 1) desc 
LIMIT 20

或

SELECT `ViewCounterView`.`id`, `ViewCounterView`.`referer`, 
(COUNT(`ViewCounterView`.`id`)) AS `ViewCounterView__referer_count`, 
(LOCATE("http", `ViewCounterView`.`referer`) >= 1) AS `ViewCounterView__external` 
FROM `dogmatic69`.`view_counter_views` AS `ViewCounterView` 
WHERE `ViewCounterView`.`referer` IS NOT NULL 
GROUP BY `ViewCounterView`.`referer` 
ORDER BY ViewCounterView__referer_count desc 
LIMIT 20

ORDER BY中存在差异。在第一个例子中MySQL会知道片段是重复的而不是再次计算，或者在第二个例子中是否使用别名来获取片段并重新计算值？

Answer 1

没有区别：MySQL每行只计算一次值。正如您在字段定义中所做的那样，它已经完成。