R sqlite：使用两个表更新给出语法错误" near "."：

Question

我想做一个更新与两个表在sqlite。

x1 <- data.frame(id = rep(1,3),
                  t = as.Date(c("2000-01-01","2000-01-15","2000-01-31"))
)
x1.h <- 0
x2 <- data.frame(id = 1, start = as.Date("2000-01-14"))

更新是:

sqldf(paste("UPDATE x1"
        ," SET x1.h = 1"
        ," WHERE EXISTS (SELECT *"
        ,"               FROM x2"
        ,"               WHERE x1.id = x2.id"
        ,"                     AND x1.t < x2.start"
        ,"               )"
        )
  )

我得到以下错误:

Error in sqliteExecStatement(con, statement, bind.data) : 
   RS-DBI driver: (error in statement: near ".": syntax error)

有人知道出了什么问题吗?谢谢你的帮助。

Answer 1

为什么使用sqldf进行更新?我认为sqldf只适用于select语句。

我将使用RSQLite。

首先我纠正你的sql语句。我更喜欢使用sep 'n'，用cat

获取漂亮的请求

str.update <- paste(" UPDATE x1"
            ," SET h = 1 "              ## here the error
            ," WHERE EXISTS (SELECT * "
             ,"              FROM x2 "             ## here second error 
             ,"              WHERE x1.id = x2.id "
            ,"               AND x1.t < x2.start "
            ,"       )"
      ,sep ='n'
)

cat(str.update)
 UPDATE x1
 SET h = 1 
 WHERE EXISTS (SELECT * 
              FROM x1,x2    ##
              WHERE x1.id = x2.id 
               AND x1.t < x2.start 
       )

然后你可以这样做:

library(RSQLite)
con <- dbConnect(SQLite(), ":memory:")
dbWriteTable(con, "x1", x1)            # I create my table x1
dbWriteTable(con, "x2", x2)            # I create my table x2
res <- dbSendQuery(con, str.update)   
dbReadTable(con,name='x1')            ## to see the result

编辑

我在Op澄清后编辑了我的答案(FROM x1,x2变成FROM x2)

Answer 2

我找到了这个解决方案:

x1$h <- 0
x1 <- sqldf(c("UPDATE x1
        SET h = 1
        WHERE EXISTS (SELECT x1.id
                        FROM x2
                        WHERE x1.id = x2.id
                          AND x1.t < x2.start
                     )",
        "SELECT * FROM main.x1"))

给:

> x1
  id          t h
1  1 2000-01-01 1
2  1 2000-01-15 0
3  1 2000-01-31 0

来源:https://code.google.com/p/sqldf/8. _why_am_i_having_problems_with_update ?其他需要提醒的事情:显然别名不起作用，例如UPDATE x1 a…谢谢你的帮助。

Answer 3

我认为你的内部SELECT没有说它从哪里选择。单独试试吧。我认为它应该看起来更像:

SELECT * FROM x1,x2 WHERE x1.id = x2.id AND x1.t < x2.start