Question

我使用RSQLite访问一个简单的SQLite数据库来返回一组已定义的数据。我希望能够限制查询，以便通过限制分类字段仅返回数据的子集。

我已经编写了一个函数，我希望能够提供在where子句中使用的参数，但是当我以这种方式运行它并将值作为参数时，我不断得到一个＆＃39;对象＆＃39; AAPL＆＃39;发现错误＆＃39; （其中参数是AAPL）。

通过对我希望在函数中限制的值进行硬编码，它可以正常工作，并且运行f2(5)将返回前五行＆＃39; AAPL＆＃39;

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) "

任何帮助都会感激不尽，因为我对此感到有些沮丧。

Answer 1

stockName应该在引号中：

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

这也应该有效：

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

使用RSQLite的R中的分类变量的Where子句

1 个答案: