r - 使用RSQLite的R中分类变量的where子句

Question

我正在使用RSQLite访问简单的SQLite数据库以返回定义的数据集。我希望能够限制查询，以便通过限制类别字段仅返回数据的子集。

我编写了一个函数，希望能够提供在where子句中使用的参数，但是当我以值作为参数运行该函数时，我不断收到“对象'AAPL'发现错误” （其中参数为AAPL）。

通过硬编码要在函数中限制的值，它可以正常工作，运行f2(5)将返回'AAPL'的前5行

f2 <- function(n, stockName) {

  library(RSQLite)

  conSQLiteParallel <- dbConnect("SQLite", dbname="stocks.sqlite")
  ## this sql works fine
  sqlcmdParallel <- paste("SELECT stock, gain ",
      "FROM stock_gains ",
      "WHERE day <=", n, " and stock ='AAPL'", sep="")
  resultsHandleParallel <- dbSendQuery(conSQLiteParallel, sqlcmdParallel)

  d <- fetch(resultsHandleParallel)
}

results <- f2(5)

但是，当我尝试使用stockName变量将值传递给函数时，它给了我

f2 <- function(n, stockName) {

    library(RSQLite)
    conSQLiteParallel <- dbConnect("SQLite", dbname="stocks.sqlite")
    ## this sql does not work correctly, but only gives an error 
    ## when running the function
    sqlcmdParallel <- paste("SELECT stock, gain ",
        "FROM stock_gains ",
         "WHERE stock =", stockName, sep="")
    resultsHandleParallel <- dbSendQuery(conSQLiteParallel, sqlcmdParallel)

    d <- fetch(resultsHandleParallel)
}

results <- f2(5,APPL) - gives the error "Error in paste("SELECT stock, gain FROM stock_gains WHERE stock =", stockName,  : 
  object 'APPL' not found"

results <- f2(5,'APPL') - gives the error "Error in sqliteExecStatement(conn, statement, ...) : 
  RS-DBI driver: (error in statement: no such column: APPL) "

results <- f2(5,distinctStocks[1,1]) - gives the error "Error in sqliteExecStatement(conn, statement, ...) : 
  RS-DBI driver: (error in statement: no such column: AAPL) "

如有任何帮助，我们将不胜感激，不胜感激。

Answer 1

stockName应该用引号引起来：

paste0("SELECT stock, gain FROM stock_gains WHERE day <= ", n, 
       " and stock = '", stockName, "'")

这也应该起作用：

library(gsubfn)
fn$identity("SELECT stock, gain 
             FROM stock_gains 
             WHERE day <= $n and stock = '$stockName'")