我正在分析一个相当可怕的遗留数据库/代码库,尝试通过将查询组合到连接中来减少服务器负载(包括通常调用超过一百万个单独查询的电子邮件警报cron作业).
SELECT * FROM
class_alerts_holding ah
INNER JOIN class_listings l ON l.id = ah.lid
INNER JOIN class_users u ON u.id = ah.uid
LEFT JOIN class_prodimages pi ON pi.pid = ah.lid
吐出120列......
aid | id | lid | uid | oid | catName | searchtext | alertfreq | listType | id | owner | title | section | shortDescription | description | featured | price | display | hitcount | dateadded | expiration | url | notified | searchcount | repliedcount …我正在尝试为data.frame中的每个变量名添加一个公共前缀.例如,使用mtcars数据,我可以添加前缀"cars".使用以下代码:
> data(mtcars)
> names(mtcars)
[1] "mpg" "cyl" "disp" "hp" "drat" "wt" "qsec" "vs"
[9] "am" "gear" "carb"
> names(mtcars) <- paste0("cars.", names(mtcars))
> names(mtcars)
[1] "cars.mpg" "cars.cyl" "cars.disp" "cars.hp"
[5] "cars.drat" "cars.wt" "cars.qsec" "cars.vs"
[9] "cars.am" "cars.gear" "cars.carb"
但是,我想%>%使用一些dplyr语法将其作为管道操作的一部分(即,使用串联的一系列函数).这似乎是一些组合rename和everything()应该做的伎俩,但我不知道如何让它工作.有没有人有任何想法？