Can I gracefully include formatted SQL strings in an R script?

Question

I\'m working in an R script that uses a long SQL string, and I would like to keep the query relatively free of other markup so as to allow copying and pasting between editor

Answer 1

A graceful way of "including" a long SQL query is to keep it in a separate .sql file. Preferably somewhere it can be syntax highlighted, a text file in RStudio will do the job. You can then in your main R script read the file into a string and populate it with variables using one of the many "named" sprintf-type solutions, such as infuser.

.sql

select *
from mytable
where id = {{a}} 
and somevar = {{b}}

.R

library(readr)
library(infuser)

query <- read_file("query.sql") %>%
         infuse(a = 1, b = 2) 

Answer 2

If you're an old C programmer from way back, as I am, you might enjoy just using sprintf().

Borrowing Ian's example:

y<-"y1"
x<-"somethingorother"
query <- sprintf(
'SELECT DISTINCT x AS %s,
                 y AS %s,
 FROM tbl
 WHERE id=%%s
 AND num=%%d', x, y)

yields:

> cat(query,"\n")
SELECT DISTINCT x AS somethingorother,
                 y AS y1,
 FROM tbl
 WHERE id=%s
 AND num=%d 

Answer 3

I've ended up simply hitting the sql string with sql <- gsub("\n","",sql) and sql <- gsub("\t","",sql) before running it. The string itself can be as long as it needs to be, but stays free of any concatenation markup.

Answer 4

I'd recommend just using a plain string, and not embedding variable values into it. Use placeholders instead.

sql <- "SELECT foo FROM bar
    WHERE col1 = ?
    AND col2 = ?
    ORDER BY yomama"

I'm not sure if the double-quote is the best way to embed multi-line strings in R code (is there something like here-docs?), but it does work, unlike in Java.

Is there some reason you don't want to send "\n" or "\t" to your database? They should be fine in the SQL.

Answer 5

you can override the %+% operator to have better string concatination syntax:

'%+%' <- function(x,y) paste(x,y,sep="")

y<-"y1"
x<-"somethingorother"
query<-
'SELECT DISTINCT x AS ' %+% x %+%',\n'    %+%
'                y AS ' %+% y %+% '\n'    %+%
' FROM tbl
 WHERE id=%s
 AND num=%d'

cat(query,"\n")

yields:

> cat(query,"\n")
SELECT DISTINCT x AS somethingorother,
                y AS y1
 FROM tbl
 WHERE id=%s
 AND num=%d