使用交叉应用-如何联接表以交叉应用联接

Question

我如何重新加入从 ### First, create data.frame from "complete" csv files ### folder_complete <-"insert path here" df_list_complete <- list.files(path=folder_complete, pattern="*.csv", full.names = TRUE) df_complete = ldply(df_list_complete, read_csv) ### Then, read in and edit "incomplete" files one at a time using for loop ### ### Note "incomplete" files are in a different director - this was set during the session ### filenames <- dir(pattern = "*.csv") for (i in 1:length(filenames)) { tmp <- read.csv(filenames[i], stringsAsFactors = FALSE) ### Merge / Identify matches between "complete" data.frame and "incomplete" file ### ### using "Programme Synopsis" as the unique column ### tmp_new <- merge(tmp, df_complete, by = "Programme_Synopsis") ### Delete any rows with NAs in specific columns - ### ### I did this because the previous step matched empty rows for these columns, and I didn't want these ### tmp_new <- distinct(tmp_new,Programme_Synopsis_url.x, .keep_all = TRUE) tmp_new <- distinct(tmp_new,Programme_Duration.y, .keep_all = TRUE) ### Delete Duplicate columns - merging created several duplicate columns (.y, .x) ### ### I only wanted to add the matching "Programme Duration" column from the "complete" data.frame to the "incomplete" file ### ### but wasn't sure how to do this. ### ### Instead, I had to retrospectively remove the duplicate columns ### tmp_new <- tmp_new[ -c(2:7) ] ### Rename columns ### tmp_new2 <- rename(tmp_new, c("Programme_Synopsis_url.y" = "Programme_Synopsis_url", "Programme_Duration.y" = "Programme_Duration", "Programme_Category.y" = "Programme_Category", "Programme_Availability.y" = "Programme_Availability", "Programme_Genre.y" = "Programme_Genre", "Programme_Title.y" = "Programme_Title")) ### Merge (again!) using plyr Join function ### df <- join(tmp_new2, tmp, by = "Programme_Synopsis_url", type = "full") ### Delete any without an index ### ### (i.e. those that don't belong in this dataframe) ### df <- df[!is.na(df$index), ] ### Re-order by original index ### df <- df[order(df$index), ] ### Remove duplicated index columns ### df$index.x <- NULL df$index.y <- NULL ### Write out the new file ### write.csv(df, filenames[[i]], row.names = FALSE) 作为value返回的值？

以下代码将以CSV格式存储的值存储在单个列中，并使用STRING_SPLIT（）将其拆分为表形式返回。我只是想重新加入这些值，因为它们处于“表格形式”。目前，我只能通过在查询下方使用另一个CTE（将这些逗号分隔的值分开）来执行此操作。我很确定可以只需要联接表数据而无需其他CTE。

以下使用CTE生成伪造数据的代码。可重现

CROSS APPLY

显示问题的Gif

Answer 1

我不敢相信，但是答案是如此简单，我几乎不好意思问了我。基本上，我只需要别名STRING_SPLIT（）函数返回的表即可。我只是没有想到将函数作为表使用，但是由于它以表的形式返回，因此可以对它进行别名，然后再利用其中的字段。

这里的关键是别名：

CROSS APPLY STRING_SPLIT(fd.multi_select, ',')为其提供别名csv。

下面的新代码显示了如何执行此操作：

WITH fake_data AS
(
    SELECT 1 as pkey, 'Billy' as name, 'FE,BF,AF,JF,AA' AS multi_select
)
, lookupTable AS
(
    SELECT 'Forever'   AS lookupValue, 'FE' AS lookupItem UNION ALL
    SELECT 'BoyFriend' AS lookupValue, 'BF' AS lookupItem UNION ALL
    SELECT 'AsFriend' AS lookupValue, 'AF' AS lookupItem
)

SELECT fd.pkey, fd.name, value
FROM fake_data fd
    CROSS APPLY STRING_SPLIT(fd.multi_select, ',') csv
    LEFT JOIN lookupTable lt ON lt.lookupItem = csv.value