Question

我需要生成复杂的select语句，每次运行脚本时，这些语句都会根据输入文件而变化。

我有一个名称列表作为我的过滤器列表，并且我有一个在另一线程中建议我使用的select语句。我不确定如何在接下来的6个小时中不用坐在Google上就可以生成所需的内容。

我需要为列表中的每个项目创建一个MAX（CASE ...）行。

list <- df$names

list:
1  square
2  ball
3  dog
4  triangle
5  hamster
6  circle
7  yellow
8  cat

suggested SELECT format:
SELECT 
   data.loc
 , data.type
 , MAX(CASE WHEN data.name = 'cat' THEN 1 ELSE 0 END) AS cat
 , MAX(CASE WHEN data.name = 'hamster' THEN 1 ELSE 0 END) AS hamster
FROM 
 data
GROUP BY 
   data.loc
 , data.type

我相信期望的输出将是：

SELECT 
   data.loc
 , data.type
 , MAX(CASE WHEN data.name = 'square' THEN 1 ELSE 0 END) AS square
 , MAX(CASE WHEN data.name = 'ball' THEN 1 ELSE 0 END) AS ball
, MAX(CASE WHEN data.name = 'dog' THEN 1 ELSE 0 END) AS dog
, MAX(CASE WHEN data.name = 'triangle' THEN 1 ELSE 0 END) AS triangle
, MAX(CASE WHEN data.name = 'hamster' THEN 1 ELSE 0 END) AS hamster
, MAX(CASE WHEN data.name = 'circle' THEN 1 ELSE 0 END) AS circle
, MAX(CASE WHEN data.name = 'yellow' THEN 1 ELSE 0 END) AS yellow
, MAX(CASE WHEN data.name = 'cat' THEN 1 ELSE 0 END) AS cat
FROM 
 data
GROUP BY 
   data.loc
 , data.type

Answer 1

我能想到的最简单的方法是

l <- list("Cat", "dog", "bird")
sqlqry <- "SELECT 
   data.loc
 , data.type"
for (i in 1:length(l)) {
  sqlqry <- paste0(sqlqry, sprintf(", MAX(CASE WHEN data.name = '%s' THEN 1 ELSE 0 END) AS %s",l[i], l[i]))
  print(sqlqry)
}
sqlqry <- paste0(sqlry, "your where clause")

R生成mysql选择语句

1 个答案: