queryparser

queryparser translates SQL queries into lists of unevaluated R expressions.

⚠️ Most R users should not directly use queryparser. Instead, use it through tidyquery.

For an introduction to tidyquery and queryparser, watch the recording of the talk “Bridging the Gap between SQL and R” from rstudio::conf(2020).

Installation

Install the released version of queryparser from CRAN with:

install.packages("queryparser")

Or install the development version from GitHub with:

# install.packages("remotes")
remotes::install_github("ianmcook/queryparser")

Usage

Call the function parse_query(), passing a SELECT statement enclosed in quotes as the first argument:

library(queryparser)

parse_query("SELECT DISTINCT carrier FROM flights WHERE dest = 'HNL'")
#> $select
#> $select[[1]]
#> carrier
#> 
#> attr(,"distinct")
#> [1] TRUE
#> 
#> $from
#> $from[[1]]
#> flights
#> 
#> 
#> $where
#> $where[[1]]
#> dest == "HNL"

Queries can include the clauses SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, and LIMIT:

parse_query(
" SELECT origin, dest,
    COUNT(flight) AS num_flts,
    round(SUM(seats)) AS num_seats,
    round(AVG(arr_delay)) AS avg_delay
  FROM flights f LEFT OUTER JOIN planes p
    ON f.tailnum = p.tailnum
  WHERE distance BETWEEN 200 AND 300
    AND air_time IS NOT NULL
  GROUP BY origin, dest
  HAVING num_flts > 3000
  ORDER BY num_seats DESC, avg_delay ASC
  LIMIT 2;"
)
#> $select
#> $select[[1]]
#> origin
#> 
#> $select[[2]]
#> dest
#> 
#> $select$num_flts
#> sum(!is.na(flight))
#> 
#> $select$num_seats
#> round(sum(seats, na.rm = TRUE))
#> 
#> $select$avg_delay
#> round(mean(arr_delay, na.rm = TRUE))
#> 
#> attr(,"aggregate")
#>                      num_flts num_seats avg_delay 
#>     FALSE     FALSE      TRUE      TRUE      TRUE 
#> 
#> $from
#> $from$f
#> flights
#> 
#> $from$p
#> planes
#> 
#> attr(,"join_types")
#> [1] "left outer join"
#> attr(,"join_conditions")
#> attr(,"join_conditions")[[1]]
#> f.tailnum == p.tailnum
#> 
#> 
#> $where
#> $where[[1]]
#> (distance >= 200 & distance <= 300) & !is.na(air_time)
#> 
#> 
#> $group_by
#> $group_by[[1]]
#> origin
#> 
#> $group_by[[2]]
#> dest
#> 
#> 
#> $having
#> $having[[1]]
#> num_flts > 3000
#> 
#> 
#> $order_by
#> $order_by[[1]]
#> -xtfrm(num_seats)
#> 
#> $order_by[[2]]
#> avg_delay
#> 
#> attr(,"aggregate")
#> [1] FALSE FALSE
#> 
#> $limit
#> $limit[[1]]
#> [1] 2
#> 
#> 
#> attr(,"aggregate")
#> [1] TRUE

Set the argument tidyverse to TRUE to use functions from tidyverse packages including dplyr, stringr, and lubridate in the R expressions:

parse_query("SELECT COUNT(*) AS n FROM t WHERE x BETWEEN y AND z ORDER BY n DESC", tidyverse = TRUE)
#> $select
#> $select$n
#> dplyr::n()
#> 
#> attr(,"aggregate")
#>    n 
#> TRUE 
#> 
#> $from
#> $from[[1]]
#> t
#> 
#> 
#> $where
#> $where[[1]]
#> dplyr::between(x, y, z)
#> 
#> 
#> $order_by
#> $order_by[[1]]
#> dplyr::desc(n)
#> 
#> attr(,"aggregate")
#> [1] FALSE
#> 
#> attr(,"aggregate")
#> [1] TRUE

queryparser will translate only explicitly allowed functions and operators, preventing injection of malicious code:

parse_query("SELECT x FROM y WHERE system('rm -rf /')")
#> Error: Unrecognized function or operator: system

Current Limitations

queryparser does not currently support:

queryparser currently has the following known limitations:

Non-Goals

queryparser is not intended to:

The sqlparseR package (CRAN) provides a wrapper around the Python module sqlparse.