在 R 脚本中传递字符串变量以在 SQL 语句中使用它

Question

I tried use a string variable in R script to use through SQL statement for example:

x="PASS"

SQL<- paste("select ID, NAME, STATUS from STUDENT where STATUS =(",x,")",sep="")
Q1 <- dbGetQuery(con, SQL)

The ERROR says:

Error in mysqlExecStatement(conn, statement, ...) :
RS-DBI driver: (could not run statement: Unknown column 'PASS' in 'where clause')

That means STATUS =(",x,")" = PASS and it must 'PASS' with add quote ''

I tried to put the '' but no success as the following.

SQL <- paste("select ID, NAME, STATUS from STUDENT where STATUS ='(",x,")' ",sep="")
Q1 <- dbGetQuery(con, SQL)

I tested it with number and it is work well but when I use string it is not working, because the value must be in quotes ' ' .

Answer 1

Use sprintf instead:

x <- "PASS"
sprintf("select ID, NAME, STATUS from STUDENT where STATUS = '%s'", x)

## [1] "select ID, NAME, STATUS from STUDENT where STATUS = 'PASS'"

Answer 2

Try this:

library(gsubfn)
x <- "PASS"

fn$dbGetQuery(con, "select ID, NAME, STATUS from STUDENT where STATUS = '$x' ")

This also works:

s <- fn$identity("select ID, NAME, STATUS from STUDENT where STATUS = '$x' ")
dbGetQuery(con, s)

Answer 3

EDIT for windows

Try

x = "PASS"

SQL<- paste0("select ID, NAME, STATUS from STUDENT where STATUS = ", shQuote(x, 'sh'))
Q1 <- dbGetQuery(con, SQL)

More generally shQuote is useful for constructed things like:

paste0("SELECT * FROM urtable where urvar IN(", paste0(shQuote(LETTERS, 'sh'), collapse = ','), ")")
[1] "SELECT * FROM urtable where urvar IN('A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z')"

 #

If you have simple character strings. For more complicated character strings other approaches maybe necessary. For example in PoSTgreSQL you can use Dollar-Quoted String Constants to escape characters.

You dont mention what variant of SQL you are using or associated R package. Some R packages may have helper functions like postgresqlEscapeStrings in RPostgreSQL or dbEscapeStrings in RMySQL .

Answer 4

Use glue_sql() from glue package.

x = "PASS"

glue_sql("select ID, NAME, STATUS from STUDENT where STATUS = {x}", .con = con)

see more examples here: https://glue.tidyverse.org/#glue_sql-makes-constructing-sql-statements-safe-and-easy