Question

我尝试了以下查询：

studentcal3 <- function(x,y)
{
i<- x
print(i)
j <- y
 print(j)
demo1 <-sqldf("SELECT a.StudentName, (b.marks/a.marks) as difference from 
(select Date, StudentName, marks from studenthistorydemo WHERE Date= i) as a 
INNER JOIN (select Date, StudentName, marks from studenthistorydemo where 
 Date= j) as b on a.marks= i and b.marks= j  WHERE a.marks = i and b.marks = 
j and a.StudentName=b.StudentName")
 }

然后调用函数

studentcal3('2014-01-01','2014-01-02')

错误： - rsqlite_send_query中的错误（conn @ptr，statement）：没有这样的列：i

如何解决这个问题？ P.S - 我是R的新手

Answer 1

引擎应该如何知道，哪些部分是外部变量？您必须使用字符串连接（Read about paste()）。请注意，您必须在单引号内以及与文化和语言无关的格式传递变量！

  studentcal3 <- function(x,y)
  {
    i<- x
    print(i)
    j <- y
    print(j)
    cmd <-paste("SELECT a.StudentName, (b.marks/a.marks) as difference from ", 
                  "(select Date, StudentName, marks from studenthistorydemo WHERE Date='",i,"') as a ",
                  "INNER JOIN (select Date, StudentName, marks from studenthistorydemo where ", 
                  "Date='",j,"') as b on a.marks='",i,"' and b.marks='",j,
                  "' WHERE a.marks ='",i,"' and b.marks ='",j,"' and a.StudentName=b.StudentName",sep="")
    #demo1 <-sqldf(cmd)
    print(cmd)
  }
  studentcal3('2014-01-01','2014-01-02')

结果

“选择a.StudentName，（b.marks / a.marks）作为区别（选择日期，学生姓名，来自studenthistorydemo的标记 Date ='2014-01-01'）作为内部联接（选择日期，学生名称，标记来自studenthistorydemo，其中Date ='2014-01-02'）为b on a.marks ='2014-01-01'和b.marks ='2014-01-02'WHERE a.marks ='2014-01-01'和b.marks ='2014-01-02'和a.StudentName = b.StudentName“

注意sql注入！您可以构建具有真实参数的语句，以避免注入攻击。

如果这个陈述真的能提供你期望的另一个问题。您可以打印出来并将其粘贴到查询窗口中以便先测试它......

R - 如何在SQL查询中将日期作为参数传递

1 个答案: