Question

我正试图从R到MySQL数据库进行查询。查询迭代列表，因此动态更改。基于列表中每个元素的每个查询通常也会导致提取多行。我正在使用的数据库可以从这里下载：http://www.ghtorrent.org/msr14.html

在一天结束时，所有结果应该以相同的输出结束，如下所示：

pull_req_id,user,action,created_at
12359,arthurnn,opened,1380126837
12359,rafaelfranca,discussed,1380127245
12359,arthurnn,discussed,1380127676
...

我现在的代码看起来像这样，但它不起作用：

library(DBI)
library(RMySQL)

m <- dbDriver("MySQL");
con <- dbConnect(m, user='msr14', password='msr14', host='localhost',     dbname='msr14');
all_rails_projects <- dbGetQuery(con, 'SELECT * FROM projects WHERE name = "rails";')
all_rails_prs <- dbGetQuery(con, 'SELECT id FROM pull_requests WHERE     base_repo_id = 78852;')

out <- nrow(all_rails_prs)
names(out) <- as.list(all_rails_prs)

df <- c('pull_req_id', 'user', 'action', 'created_at')
out <- numeric(length(df))
names(out) <- df


for (i in nrow(all_rails_prs)) {
  SQL <- paste("select user, action, created_at from
(
select prh.action as action, prh.created_at as created_at, u.login as user
from pull_request_history prh, users u
where prh.pull_request_id ='", all_rails_prs[i,], "'", 
"  and prh.actor_id = u.id
union
select ie.action as action, ie.created_at as created_at, u.login as user
from issues i, issue_events ie, users u
where ie.issue_id = i.id
and i.pull_request_id ='", all_rails_prs[i,], "'",
"  and ie.actor_id = u.id
  union
select 'discussed' as action, ic.created_at as created_at, u.login as user
from issues i, issue_comments ic, users u
where ic.issue_id = i.id
  and u.id = ic.user_id
  and i.pull_request_id ='", all_rails_prs[i,], "'",
"union
select 'reviewed' as action, prc.created_at as created_at, u.login as user
from pull_request_comments prc, users u
where prc.user_id = u.id
  and prc.pull_request_id ='", all_rails_prs[i,], "'",
") as actions
order by created_at;", sep = "")
  res <- dbGetQuery(con, SQL)
  out[i] <- dbFetch(res, n = -1)
}

这会生成以下错误消息：

Error in (function (classes, fdef, mtable)  : 
  unable to find an inherited method for function ‘dbFetch’ for signature     ‘"data.frame"’
In addition: Warning message:
In mysqlExecStatement(conn, statement, ...) :
  RS-DBI driver warning: (unrecognized MySQL field type 7 in column 2 imported     as character)

我尝试了不同的变体，但它们都会导致某种错误，所以好像我只是没有以正确的方式设置查询结构。有人有什么建议吗？

Answer 1

根据文档，如果查询成功，dbGetQuery默认会调用fetch。

res已经是一个数据库，您可以直接将其放入out，而无需获取记录。

此外，如果您想将结果存储在数据框而不是列表中，您可能想尝试：

#get the results
res<-dbGetQuery(con, SQL)

 #if it's not null, add the request id and rbind it to the out dataframe
 if(!is.null(res)){
         out<-rbind(out,cbind(rep(all_rails_prs[i,],nrow(res)),res))
 }

您的for语法可能还有错误，您可能需要for (i in 1:nrow(all_rails_prs))

对SQL数据库进行迭代查询

1 个答案: